What would a Mitt Romney presidency be like? At one point over the summer, the candidate was offering, if elected, to “bury the hatchet” with Democrats, and his operatives are stressing how moderate and bipartisan Romney might be, even talking up how much they admire President Bill Clinton’s governing style. That might seem plausible to some, since Romney has proven himself to be quite, shall we say, flexible on his policy positions.

But such a thought ignores some powerful fixed realities in Washington — realities that will push hard against whatever urges toward moderation Romney might harbor. The most obvious is the growing partisan divide in Congress, driven especially by the GOP’s ideological turn to the right and the Tea Party’s purging of Republican moderates, a trend that the 2012 election will almost certainly accelerate. Also, as I’ve pointed out in these pages (“Campaign Promises: What They Say Is How They’ll Govern,” January/February 2012), presidents are under immense pressure from their strongest supporters to fulfill the specific policy promises they made to win the nomination, and Romney has taken positions so far to the right —for instance, not only endorsing Paul Ryan’s budget plan but putting Ryan on the ticket — as to make compromise with the Democrats almost inconceivable.

But there’s also a subtler, less noticed change in Washington that for years has been slowly undermining the capacity of administrations of both parties to compromise. Like any human organization, the White House is profoundly influenced by the nature of the people who work there, especially in senior positions. And since the 1970s, the kind of people who surround presidents has changed. In the past, they were more likely to be people whose first loyalty was to the president himself, and only secondarily, if at all, to the president’s party. In recent decades it’s become just the opposite.

Consider an illustrative contrast: Karl Rove and H. R. “Bob” Haldeman. Both helped put a president into the Oval Office and then became powerful White House advisers. But Haldeman never worked for any other politician but Nixon, while Rove, long before he went to work for George W. Bush, was an all-purpose Republican operative, having advised, among others, Texas Governor William Clements, Utah Senator Bob Bennett, and Missouri Governor John Ashcroft. What’s happened over the last few decades is that the top people around the president have, like other players in Washington, become more party connected; there are fewer like Haldeman who would not be in politics except for their relationship to the president. And there are more like Rove who are deeply connected to their party, including its wider network of elected officials, interest groups, partisan media, and think tanks, and who are therefore less likely to reach across the aisle for ideas and partnerships. The changing in the backgrounds of senior White House staffers is just one manifestation of the growing role of parties and partisanship in Washington over the last couple of generations. And of course it’s difficult to prove that any particular presidential action is tied to the influence of any particular member of the White House staff. What we can say is that a president like Richard Nixon could press forward with the formation of the Environmental Protection Agency, Amtrak, wage and price controls, the first affirmative action programs, as well as a vast expansion of Social Security, without receiving lots of opposition from his top White House aides (indeed, much of his domestic policy agenda was formulated by a Democratic aide, Daniel Patrick Moynihan).

Things began to change with Jimmy Carter’s White House. To be sure, Carter had his “Georgia Mafia”; by my count, six of the former governor’s top ten advisers — people like Hamilton Jordan and Jody Powell — had a long-term personal connection to him, and all were at least involved in the presidential campaign. But already in that era, half had broader Democratic Party ties. Stuart Eizenstat, for example, had worked in the Johnson White House and Hubert Humphrey’s 1968 presidential campaign before moving to Georgia and then starting to work for Carter; the politics office was headed by Timothy Kraft, who had worked for the New Mexico Democrats before Carter’s presidential campaign. After Carter, those with the best access to the Oval Office were even more likely to have careers independent of the president. Ronald Reagan, too, had men like Ed Meese, Michael Deaver, and Martin Anderson who had been with him in Sacramento. But they had to compete for influence in the Reagan White House with people like James Baker, David Stockman, and David Gergen, who had their own power bases in the GOP long before they hooked up with Reagan.

Similarly, Bill Clinton brought a number of loyalists from Arkansas, such as Mack McLarty, Webb Hubbell, and Vince Foster, into his administration. But power in the Clinton White House quickly gravitated to aides like George Stephanopoulos and Leon Panetta, who were established Washington players before Clinton got to town. Fully thirteen of the fifteen top staffers in the early Clinton White House had broad ties to the Democratic Party before they went to work for Clinton, while only eight of the fifteen had been with Clinton during his first presidential campaign or earlier.

The same pattern holds for the presidents who succeeded Clinton. Of the thirteen top White House aides to George W. Bush, only five had personal ties to the president prior to the 2000 campaign. Most of the rest — people like Political Director Ken Mehlman and Press Secretary Ari Fleisher — were longtime GOP professionals. Of Barack Obama’s fifteen top administration advisers, only four— David Axelrod, Peter Rouse, Valerie Jarrett, and Robert Gibbs — were involved with Obama before his first presidential campaign.

And so it goes with Mitt Romney. Only a handful of his campaign advisers — Eric Fehrnstrom, Beth Myers, and Peter Flaherty are prominent examples — go back with him even as far as his days as Massachusetts governor. And among those who have been with him the longest, most have built their careers working for other Republican politicians or operatives. So, for example, Myers worked with Karl Rove in Texas long before Romney entered politics; Fehrnstrom was active in Massachusetts Republican politics long before he signed on with Romney; and top foreign policy adviser Dan Senor served in George W. Bush’s administration and has deep ties to Washington’s neoconservative think tank apparatus. Meanwhile, Romney also has many key advisers who have no previous connections to him. Senior adviser Ron Kaufman was George H. W. Bush’s White House political director. Yet another senior adviser, Bob Wickers, was with Mike Huckabee in 2008.

What does that suggest about Romney, should he be elected? Of course, it’s too early to know who among his longtime associates and campaign advisers will win top jobs in a Romney administration, and we certainly don’t know how the power positions will shift over time.

To the extent that we can tell, however, it seems likely that Romney’s executive office, including White House staff, would be just as tied in to his party’s network as that of any recent president. While a somewhat greater proportion may be personally connected to Romney than is the case with, say, Obama—whose personal network coming into office was not nearly as extensive as Romney’s is — there’s no reason to expect any real distance between him and the Republican Party network. We’re not seeing, in personnel, anything that even remotely hints at, for example, an attempted Bain takeover of the executive branch. The bottom line is that it is far more likely that a Mitt Romney presidency will be defined by the Republican Party than that he will define his party.

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Jonathan Bernstein is a political scientist who writes about American politics, especially the presidency, Congress, parties, and elections.