THE GOP’S GROWN-UP CONTINGENT SPEAKS UP…. Republican presidential hopeful Mitt Romney pretended to understand foreign policy and national security this week, publishing an op-ed trashing the New START treaty, which he characterized as President Obama’s “worst foreign policy mistake yet.” Romney’s argument was a “thoroughly ignorant” attempt.

Yesterday, to his enormous credit, a leading Senate Republican was willing to call Romney out publicly on his pathetic display.

Senator Richard G. Lugar, one of the Republican Party’s senior voices on foreign affairs, fired back Thursday at Mitt Romney over his opposition to the new nuclear treaty with Russia, accusing Mr. Romney of “hyperbolic” rhetoric that is divorced from the reality of arms control.

In an unusually harsh statement, Mr. Lugar said Mr. Romney “repeated discredited objections” to the treaty and “appears unaware of arms control history and context.” The senator said rejecting the treaty, as Mr. Romney has urged, would mean giving up any human monitoring of Russia’s nuclear arsenal and guarantee no follow-up agreement to further limit nuclear weapons.

“Governor Romney offers additional misreadings and myths that have been refuted explicitly in Congressional hearings,” said Mr. Lugar, the ranking Republican on the Senate Foreign Relations Committee.

It was fairly devastating. Lugar, a conservative senator and the former chairman of the Senate Foreign Relations Committee, not only highlighted a variety of Romney claims that were patently false, but even suggested the former one-term governor’s logic was flawed. Lugar did everything short of calling Romney a shameless, foolish hack — and he almost did that.

It’s exceedingly rare for respected, seasoned Republican senators to call out leading party voices like this, which made Lugar’s remarks that much more important.

Michael Crowley argued, “What you’re seeing, it seems to me, is a struggle between the GOP’s old-guard national security center and an resurgent, post-Iraq hawkish right wing — one that also includes Sarah Palin. The ambitious national politicians are driving the party’s agenda to places the seasoned experts don’t think it should go.”

That sounds about right, but it’s worth emphasizing that the two competing Republican wings are not engaged in a genuine debate — one of these wings simply has no idea what they’re talking about. This isn’t moderates vs. wingnuts, pragmatists vs. idealists, or even neocons vs. realists. Rather, this is people who know something about foreign policy and national security issues vs. uninformed right-wing activists trying to impress Fox News viewers in advance of the next GOP primary.

As Lugar reminded Romney yesterday, veteran Republicans with extensive records on these issues — Brent Scowcroft, Henry Kissinger, Reagan Secretary of State George Schultz, Reagan Chief of Staff Kenneth Duberstein, Colin Powell, former Sen. Chuck Hagel (R-Neb.), Reagan Chief of Staff Howard Baker, former Sen. John Danforth (R-Mo.) — have all enthusiastically endorsed New START, and have urged Congress to ratify it. Moreover, Joint Chiefs of Staff Chairman Mullen has said the treaty has “the full support” of the uniformed military.

Romney wanted to play grown-up this week, laying the groundwork for credibility on these issues in advance of 2012. He’s failed miserably.

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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.