Mr. Kaine is a smart, articulate and principled attorney who spent much of his legal career making real the promise of open housing for people of color and people with disabilities. As a lawyer, he was a stalwart defender of civil rights and civil liberties who courageously challenged Virginia death penalty abuses.
Mr. Kaine learned to speak Spanish fluently while working with the poor in Central America and then came home to graduate with high marks from Harvard Law School. He could have gone corporate; instead, he went to the grass roots, focusing on fair-housing advocacy in Virginia and teaching legal ethics at the University of Richmond Law School.
When he entered politics, the affable contender went from strength to strength. After winning election to the Richmond City Council and then serving successfully as that city's mayor, he beat a right-wing Republican with ties to the Bush administration in an edgy race for lieutenant governor that was decided just weeks after 9/11. Four years later, he beat a former Republican state attorney general in an intense contest for governor. Smeared for his opposition to the death penalty and support for responsible fiscal policies - "raising taxes," in the language of GOP attack ads - Mr. Kaine proved to be a remarkably agile contender. He piled up votes in the liberal Washington suburbs while holding his own in rural areas, where his ability to go less Harvard and more homespun played well.
As governor, he has been both progressive and effective - maintaining the responsible approach to budgeting initiated by former Gov. Mark Warner, launching bold land conservation initiatives, making moves to bar smoking in a tobacco state where such a stance was once considered politically impossible, and responding to the Virginia Tech massacre in a caring yet conscientious manner that won wide praise.
So Mr. Kaine really is a very attractive contender for the No. 2 spot on the Democratic ticket. Unfortunately, it is unlikely that he will be Mr. Obama's running mate.
While casual commentators suggest that his addition to the ticket would put the potential swing state of Virginia into play, the reality is that Virginia is already competitive, thanks to the same shifting political demographics that have seen the state elect two Democratic governors and a Democratic senator in recent statewide contests.
Mr. Kaine's selection would require Mr. Obama to spend more time explaining his choice than this presidential candidate - or any party leader involved in a high-stakes national campaign - is inclined to do.
Mr. Kaine is a devout Catholic who cherishes the "seamless garment" pro-life arguments of the late Cardinal Joseph Bernardin, who as archbishop of Chicago advocated for the defense of all human life as part of a broad social and economic justice ethic. Unlike Mr. Obama, who is a supporter of capital punishment, Mr. Kaine has a long record of speaking and acting in opposition to the death penalty. He has presided over executions as governor - explaining that as a lawyer, he accepts even laws that go against his faith - but he has also vetoed five death penalty expansion bills. And in June, he commuted the death sentence of Percy Levar Walton - convicted and sentenced to death for three murders - to life in prison without parole. Testing showed that Mr. Walton had an IQ of 66 and may have lacked the cognitive skills to understand his crime and the punishment he faced, but that subtlety is unlikely to be highlighted in Republican attack ads.
In another deviation from Mr. Obama, Mr. Kaine expresses what he describes as a "faith-based opposition to abortion." The Virginian is strongly opposed to late-term abortion and is involved with Democrats for Life of America. While some Democrats like to fantasize that an Obama-Kaine ticket might attract votes from anti-abortion social conservatives, it could also alienate - or at least unsettle - feminists who backed Hillary Clinton and have yet to fully embrace Mr. Obama's candidacy.
Finally, Mr. Kaine has never served in the U.S. House or Senate, meaning that an Obama-Kaine ticket would have a combined three years of federal experience, no military record and limited long-term standing on the foreign policy front.
So why is there so much talk about the prospect of an Obama-Kaine ticket? Why are Obama aides feeding the fire? Why is Mr. Kaine stoking it? Simple: Mr. Kaine, a passionate proponent of racial justice throughout his adult life and a genuine believer in the prospect of "change we can believe in," was among the first prominent officials in the country to back Mr. Obama, and he worked hard and smart to prevent Mrs. Clinton from gaining ground in Virginia's February primary.
Mr. Obama owes Mr. Kaine. And the senator from Illinois genuinely likes the governor. There is a very real chance that Mr. Kaine - who is term limited and who is unlikely to have a shot at a U.S. Senate seat anytime soon - would end up in an Obama administration. And there is every reason to believe that Mr. Kaine could obtain a high-ranking spot. Indeed, with his extensive legal experience in a variety of relevant areas, he is a very attractive prospect for attorney general.
But there's a stature gap. Most Americans haven't heard of Mr. Kaine. So for the next week or so, he will be much talked about as a vice presidential prospect. That will garner Mr. Obama good headlines in Virginia, and it will make Mr. Kaine a national persona. Ultimately, though, Mr. Obama is likely to select a running mate with more federal and foreign experience.
But the talk of an Obama-Kaine ticket will have served both men - not to mention the administration in which the two may yet serve together.
John Nichols is Washington correspondent for The Nation magazine.