President Obama obviously faces a difficult (though far from hopeless) battle for reelection. What is less obvious from reading campaign coverage at this point in the election cycle is that, if he fails, it is also unlikely that his party will be able to retain its Senate majority or retake the House. There are twenty-three Democratic-held Senate seats up for contest next November to only ten Republican. Record- low approval ratings for the GOP Congress may mean some Democratic pickups in the House. But GOP gains at the state level in 2010 have given them enough control in enough states to dominate redistricting in a way that has built firewalls around some of their most vulnerable House members. The rest comes down to turnout: if enough conservative voters show up at the polls to unseat Obama, chances are they will have the same advantage in doing damage to Democrats in Congress.

If Obama loses, Republicans will probably control, if narrowly, both ends of Pennsylvania Avenue for the second time in a decade. When that last happened, under George W. Bush—with a nine-seat House majority and a tied Senate— the party succeeded in passing major tax cuts but failed to reduce the size of government or roll back the welfare state, despite riding into town on its usual small-government rhetoric. So too during the Reagan years, when the White House and the Senate (though not the House) were in Republican hands. During both these periods of GOP dominance, entitlement and other programs grew substantially.

The question is, would this time be different? We believe the answer is yes, because of the Republican Party’s shift to the right and its demonstrated willingness to bend, break, or change legislative rules and customs that have stood in the way of radical change in the past.

This will be the case even if the candidate who defeats Obama is Mitt Romney—in our view the only plausible contender in the Republican field who could conceivably garner the nomination and prove an acceptable alternative to the incumbent. (And it would most surely be the case if Gingrich, a proven radical, becomes the nominee and, by some fluke, beats Obama.) While Romney is sufficiently protean in his ideological positioning and stance on particular issues to introduce some uncertainty over precisely what he would attempt to accomplish in office, his recent speeches have outlined a policy agenda well outside the old mainstream and wholly in sync with the new Zeitgeist of his party. Romney is now no less conservative in his positions on taxes, spending, Medicare and Medicaid, the Affordable Care Act, financial regulation, and the overall role of government than his contenders for the presidential nomination and the party establishment in Congress.

Whoever is the standard-bearer, a Republican victory in 2012 would do nothing to reverse or restrain the radically rightward march of the party. The Tea Party movement has accelerated a process that has been under way for many years within the GOP, which is now firm in its identity as the insurgent party, set upon blowing up policies and public responsibilities that enjoyed bipartisan support for many decades. The Democrats are the status quo party— protective and pragmatic. The asymmetric polarization of the two camps is the most significant feature of contemporary American politics.

A President Romney would be in a poor position upon taking office to change the course outlined in his campaign. He is already suspected as an infidel by many Republican activists. His fiscal policy would almost certainly be ambitious, one not unlike the budget resolution written by Representative Paul Ryan and passed by House Republicans. Indeed, this is the course Romney has taken with his professed economic plan, released in early November. If Romney tried to dilute his own proposal, he would be met at the beginning of his presidency with a full-scale revolt on his hands from his own party, both in and out of Congress.

So here is one plausible governing scenario for 2013: After an election in which Republicans prevail, a lame-duck President Obama in December of 2012 lets all the Bush tax cuts from 2001 and 2003 expire. Starting in January of 2013, House Republicans begin a process not only to reinstate all those tax cuts but to forcefully roll back government. Though the 2012 elections have shrunk the House’s Republican majority, that majority is also farther to the right because many of its members are Tea Party types who barely survived tough primary fights from challengers who accused them of having “gone Washington”—that is, voted for a continuing resolution or a debt limit deal. As a result, Speaker John Boehner’s clout is even more eclipsed by “Young Guns” Eric Cantor, Kevin McCarthy, and Paul Ryan, making bipartisan compromises even less likely. So the House passes a budget that is akin to Paul Ryan’s plan, one that massively cuts taxes while repealing most elements of the Affordable Care Act, moving Medicare toward a premium support system for private insurance, turning Medicaid into a block grant to the states and eventually cutting its federal funding by as much as 35 percent, and enacting draconian cuts in discretionary domestic spending.

Because that bill, like the Ryan plan, would vastly widen the deficit, it runs into a problem when it moves to the Senate. According to the “Byrd Rule,” any budget bill that increases the deficit cannot be brought up under reconciliation— the process that allows budget bills to be voted on without being first subject to sixty-vote supermajority “cloture” votes. This means the legislation can be effectively bottled up if as few as forty Democrats threaten to filibuster it— which, of course, they do. Under Majority Leader Harry Reid back in the Bush and Obama years, the Senate hewed to the Byrd Rule. But the new Senate majority leader, Mitch Mc- Connell, has two precedents to rely on: the 2001 and 2003 tax cuts, both adopted under reconciliation (the latter on a 50-50 vote, with Vice President Cheney breaking the tie). He pushes the 2013 bill through reconciliation.

This move is sufficient to bring the tax-cutting parts of the budget bill up for a vote. But other parts of the legislation, including many of the Medicare changes, are still subject to cloture votes. To get these past the Democrats, McConnell faces a more daunting set of challenges. He could ignore the Byrd Rule—by appealing the ruling of the chair that the Byrd Rule applies—and thus undo it by majority vote. But that step would do more than just cause howls of outrage from Democrats and editorial writers. It would also require unanimity or near unanimity on the part of Republican senators, including several who are up for reelection in 2014, like Susan Collins, Saxby Chambliss, and Lamar Alexander, and others, like Olympia Snowe, who would object to many parts of the plan. McConnell would likely have to adjust it and dilute it some—but with what conservatives would see as a once-in-a-lifetime opportunity for revolution, he would extract the best and most extreme plan he could in order to make it happen.

Yet even with this audacious victory, some items remain on the GOP agenda that simply couldn’t be wedged into a reconciliation bill. These include changes to Social Security, repeal of financial reform, possibly the full repeal of the Affordable Care Act, and the nomination of like-minded judges. To secure these measures, McConnell’s first option, of course, is to try to win over enough Democrats to get to sixty votes, or at least get enough Democrats to make the plan appear bipartisan. That is the route George W. Bush used with tax cuts in 2001, and Max Baucus’s willingness to accommodate Bush, despite the fact that the supporters in the end numbered fewer than sixty, made the use of reconciliation at that time seem less illegitimate.

But two things have changed since 2001. First, back then filibusters were still relatively rare events; since Obama, they have become routine, applied to everything, big and small. Second, far fewer Democrats, Baucus included, will be willing to be used in this fashion now. So while there may be a few Democrats who move, far more than the forty necessary to sustain a filibuster are firm in their willingness to do so.

Faced with that roadblock, McConnell’s only other choice is to try to limit the reach of the filibuster. He will not be eager to do this. Filibuster-empowered delay tactics such as holds have become the bread-and-butter means of exerting power by many senators on both sides of the aisle. But the Senate leader quickly finds himself under immense pressure from the Wall Street Journal editorial page, Rush Limbaugh, Sean Hannity, and others to throw caution to the wind. If McConnell can find fifty votes to pass through a bill that fundamentally alters the policy landscape, eviscerating or erasing health reform and financial regulation and changing Social Security and Medicare, and confirming a slew of forty-something conservative judges who will be on the bench for decades, there is a better-than-even chance that he would succumb to temptation and erase the filibuster rule by fiat.

Would a President Romney, who, after all, has endorsed many of these elements in the course of his campaign, veto these bills? Not a chance. Would he be able, in his early days, to influence their content, perhaps by including in the Medicare plan a continuation of traditional Medicare as an option for seniors, and by adjusting the inflation levels for increasing the vouchers given to seniors? Maybe, especially since Ryan and Senator Ron Wyden announced a plan in December with those elements included. But it is very likely that Republican conservatives would seize their window of opportunity to enact at least semirevolutionary change.

Of course, there is another possibility with a Romney presidential victory: continued divided government, either because disgruntled voters throw Republicans out of their majority in the House or because they do not give Republicans the necessary three-seat gain to win a majority in the Senate. Would Romney be able to navigate through to bipartisan compromises here? For instance, could he, as a Republican president, do what Barack Obama has been unable to do: convince a significant number of Republican lawmakers to accept tax increases or defense cuts as part of a deficit-reduction plan? We are dubious. Any attempt to find common ground with Nancy Pelosi and House Democrats or Harry Reid and Senate Democrats would be met with staunch resistance by the conservatives who dominate the Republican ranks in Congress and who do not trust Romney to begin with. Alternatively, if Romney were to sign legislation passed by a Democratic Congress without significant GOP votes, he would be directly thumbing his nose at his own party’s far-right base, which holds sway over 95 percent of the Republicans in the House and at least 85 percent in the Senate. There is little in his background or current run for the nomination that suggests he has that kind of courage.

[Return to What if Obama Loses: Imagining the consequences of a GOP victory]

Our ideas can save democracy... But we need your help! Donate Now!

Thomas Mann and Norman Ornstein collaborated on this article. Mann is a senior fellow at the Brookings Institution. Ornstein is a resident scholar at the American Enterprise Institute.