Jeff Jacoby

"With all due respect," replied Brown, "it's not the Kennedy seat, and it's not the Democrats' seat. It's the people's seat." It was a pitch-perfect response, delivered with Reaganesque aplomb. It may well have been the turning point in Brown's campaign. And it would never have happened if he had turned down the debate on the grounds that Vicki Kennedy might endorse Coakley. Indeed she had endorsed Coakley. What difference did it make?

Brown is one of the state's most popular politicians, and is routinely described -- even by prominent Democrats -- as a gifted retail candidate. But this was a blown opportunity to reinforce what may be his strongest selling point with Massachusetts voters: his reputation for bipartisanship.

Brown touts his ability to work with senators on both sides of the political aisle, and there is evidence to back him up. An analysis of Senate roll calls published in January by Congressional Quarterly identified Brown as second only to Maine's Susan Collins in his willingness to cross party lines on controversial votes: In 2011, CQ reported, Brown lined up with the GOP 54 percent of the time, but with the Obama administration 70 percent of the time. Using a different formula, the Boston Globe recently calculated that on the "most important, news-generating votes," Brown has voted against the Republican leadership 24 percent of the time. "He has, in fact, demonstrated ideological flexibility," observed the Globe.

Speaking at Bunker Hill Community College last month, Brown insisted that he is not the type of person "to divide people up into easy categories – assuming the best because they agree with me, or the worst because they don't. Especially in politics, I've found it's the only way to operate." Brown could have strengthened that claim by accepting Vicki Kennedy's invitation; turning it down only undercut the self-image he is at pains to promote.

To be clear, neither Brown nor Warren is refusing to debate: The candidates have already agreed to at least three televised face-offs, including one sponsored by a media consortium that includes the Globe. Nor is the debate over the debates likely to sway many votes on Election Day. But the episode is one more sad reminder of how easy it can be to view everything through a partisan lens, and to assume that the best gauge of someone's integrity is the "R" or "D" after his name.

Jeff Jacoby

Jeff Jacoby is an Op-Ed writer for the Boston Globe, a radio political commentator, and a contributing columnist for