In the time they have served together in the United States Senate, John McCain and Barack Obama developed neither a friendship nor an intense dislike. They entered this campaign as relative strangers, and now - as the sniping builds to a steady staccato - each of them has acquired a strong sense of grievance about the other.
That, at least, is the clear impression I received from doing back-to-back, one-on-one interviews with the two prospective nominees. They are striving to keep their contest from becoming overtly personal. But it is a struggle. McCain complained bitterly to me about accusations that he has run a racist campaign, and Obama voiced his anger at the charge that he would rather lose a war than jeopardize his election.
Talking with them, I realized that they have little in shared experience on which to build a relationship. The 25-year difference in their ages is exceptionally wide for opposing candidates. McCain was already an established figure - a committee chairman and former presidential candidate - when Obama came to Washington a little less than four years ago. They serve on none of the same committees and rarely have collaborated on legislation.
On the other hand, there were few direct personal clashes. Both of them remembered only two - the same two.
The first occurred in February 2006. Obama had joined members from both parties in a group organized by McCain to draft bipartisan legislation on ethics and lobbying reform, after McCain's hearings on the Jack Abramoff scandal. But when other Senate Democrats decided to write their own bill, Obama aligned himself with them.
McCain told me, "He went off and voted with (Minority Leader) Harry Reid on the Democratic substitute. And I wrote him the now-famous letter."
The letter he sent Obama began with this stinging sentence: "I would like to apologize to you for assuming that your private assurances to me regarding your desire to cooperate in our efforts to negotiate bipartisan lobbying reform legislation were sincere." It continued, "I'm embarrassed to admit that after all these years in politics, I failed to interpret your previous assurances as typical rhetorical gloss routinely used in politics to make self-interested partisan posturing appear more noble."
Obama wrote back that he had "no idea what has prompted your response." He told me the other day: "That was one incident where he thought I had undercut him. I had a completely different view of it."
The second occurred in June 2007, during Senate floor debate on the immigration bill. One key piece of the bill authorized a guest-worker program, which was unpopular with unions, who saw the immigrants as threats to their jobs. McCain told me that Obama had become part of a bipartisan group, led by Sen. Edward Kennedy and himself, whose members understood "we had to take tough votes, sometimes against the majority of our own party, in order to preserve the coalition." But when an amendment was offered to "sunset" that part of the bill after five years, it was viewed as a "killer amendment."
"Obama went out and voted with the unions," McCain told me. McCain and Kennedy lost by one vote.
When I asked Obama to respond, he said, "When colleagues disagree on an issue, the notion that it's cause for attack is mistaken. I felt very strongly that the guest-worker program was not in the best interests of the country. I voted against it; he voted for it. ... I respect Senator McCain's right to take positions different than mine. What I don't do is abuse his integrity for doing so."
Despite these incidents, I found there is mutual respect. When we talked, Obama did not gush about McCain, but he said, "We can disagree on issues without trying to tear down the other person's reputation or attack his character."
McCain seemed genuinely impressed by his opponent. He said he had watched tapes of the Democratic debates and thought Obama had been "superb."
"He has my admiration and respect," McCain Said. "This is a person who has engaged and energized millions of Americans who had never been engaged in the political process."
No one else can lift this campaign out of the gutter, but these two are still capable of giving the country the kind of contest the voters deserve - if they can build a little mutual trust.
McCain's offer of weekly joint town meetings still stands. It is not too late for Obama to change his mind and take up this historic offer.
E-mail nationally syndicated columnist David Broder at email@example.com.