BROACHING THE INVIOLABLE MOTIVATIONS LINE…. E.J. Dionne Jr. considers Senate Republicans’ tactics on blocking ratification of the pending arms treaty, New START, and concludes that Sen. Jon Kyl (R-Ariz.) and his cohorts are “playing Russian roulette with our nation’s interests.”

If this treaty is not ratified, the only winner will be Vladimir Putin. Is Kyl, who on “Meet the Press” Sunday reiterated his desire to delay consideration of the treaty, really willing to risk giving Putin and anti-American forces in Russia a leg up?

You don’t have to believe me on this. As [neoconservative interventionist Robert Kagan] wrote this month in The Post, defeat of the treaty will “strengthen Vladimir Putin,” who would use its demise “to stir more anti-Western nationalism, further weakening an already weak [President Dmitry] Medvedev and anyone else who stands for a more pro-Western approach.” It’s not my habit to agree with [Pat Buchanan], but he’s right in saying: “Killing the treaty would morally disarm those Russians who see their future with the West.”

And the Financial Times, hardly a left-wing newspaper, noted that Kyl’s core arguments against the treaty are “so weak as to call into question Mr. Kyl’s good faith.” We don’t need more time to consider it; the treaty has been debated for months. And the Obama administration has made a slew of concessions to Kyl to modernize our nuclear program. What, besides the identity of our current president, justifies this obstruction?

I can appreciate why it’s unusual, if not downright reprehensible in some circles, to question politicians’ motives. It’s the inviolable line — everyone is expected to be patriots acting in good faith, with sincere disagreements over the merits of competing policies. Without clear evidence of malicious intentions, motivations are supposed to be largely off limits in the civil discourse, especially when it comes to Republicans.

The problem with the GOP lately is that even those inclined to give the party the benefit of the doubt simply can’t come up with a good-faith explanation for their actions — which leads to awkward questions about whether they’d actually put their partisan goals ahead of the national interest. It’s almost a modified, political version of Occam’s Razor — if one can’t come up with a reasonable explanation for a party’s actions on policy grounds, it necessarily makes questions about motivations plausible.

Dionne isn’t the only one wondering about this. Brent Scowcroft, the former national security adviser to President George H.W. Bush, can’t figure out why his own party would be acting this way, leading him to assume Republican senators are putting “the desire for the president not to have a foreign policy victory” ahead of the nation’s security interests.

AEI’s Norm Ornstein, marveling at GOP’s misconduct, said, “I cannot fathom why they are doing what they are doing.” The Washington Post Dana Milbank noted last week that Republicans appear to be “trying to weaken Americans’ security,” concluding, “To borrow Bush’s phrase, are Republicans not interested in the security of the American people?” Paul Krugman argued that the GOP is blocking ratification “not because of legitimate objections, but simply because it’s an Obama administration initiative; if sabotaging the president endangers the nation, so be it.”

If Republicans care about squelching questions about their intentions, they should probably come up with at least mildly coherent talking points. Or they could drop the nonsense and endorse ratification, but that appears highly unlikely.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.