WHEN SENATOR SCOTT BROWN turned down an invitation to debate Elizabeth Warren at the Edward M. Kennedy Institute in Boston, did he shrewdly avoid a trap? Or did he foolishly blow an opportunity?

The invitation had been extended on June 8 by Vicki Kennedy, widow of the late senator and president of the institute's board. Last week Brown agreed to take part in the debate -- but only if Kennedy promised to personally uphold "the spirit of neutrality" by not endorsing any candidate or otherwise getting involved in the race. When Kennedy wouldn't go along with that condition, Brown said no to the debate. "The Kennedy Institute cannot hold itself out as a nonpartisan debate sponsor," Brown's campaign manager insisted, "while the president of its board of trustees gets involved in the race on behalf of one of the candidates."

To hear some Republicans tell it, Brown's refusal was perfectly justified: Had he accepted Vicki Kennedy's proposal, he would have been walking into an ambush. State GOP chairman Bob Maginn applauded Brown for spurning "this charade of a debate" and exposing the Kennedy Institute's "invitation for what it was: a setup." At the popular conservative blog Red Mass Group, Republican activist Rob Eno imagined a counter-scenario: Suppose Nancy Reagan invited President Obama to debate Mitt Romney at the Ronald Reagan Presidential Library in California. Would anyone fault Obama for declining such an offer?

It's not a very convincing argument. The Kennedy Institute may be run by Democrats who idolize the late senator, but that hardly means it's incapable of impartially hosting a political debate -- a debate in which a Republican can shine.

And if anyone should know that, Brown should. When he first ran for the Senate 2½ years ago, the little-known state senator from Wrentham had no objection to squaring off against his Democratic opponent, Martha Coakley, in a televised debate sponsored by the Kennedy Institute and moderated by David Gergen. An ambush? It was anything but. The most memorable moment of the evening was Brown's now-legendary retort when Gergen asked if Brown really wanted to sit in Ted Kennedy's Senate seat and block health-care reform.