Rule #1 of the vice presidential selection process is akin to the Hippocratic Oath: first, do no harm. And with rumors swirling that Barack Obama is seriously considering first-term Virginia Governor Tim Kaine as his #2, the Democratic nominee risks breaking rule #1.

Which isn't to say that Kaine doesn't score well on some of the half-dozen metrics (such as geography, chemistry, theme, balance, experience and party solidarity) often used to assess vice presidential aspirants.

Kaine, after all, is part of the statewide Democratic wave including Mark Warner and Jim Webb which could help carry his state for Obama. And to be sure, the close relationship between Obama and Kaine - and their families - is an asset on the campaign trail and beyond. Thematically, the 50-year old Kaine like Obama is a new face in national Democratic politics and could bolster Obama's campaign of change ushered in by a new generation of leadership. Obama-Kaine '08 harkens back to the energy and relative youth of Clinton-Gore '92.

But those aren't the primary challenges Obama faces in the veepstakes. In a campaign in which John McCain and the Republican attack machine will paint Barack Obama as an inexperienced neophyte on national security issues, Tim Kaine would be a liability. A man without either military experience or involvement in defense and foreign policy at the national level, the untested Kaine would only magnify the perception Obama must battle until election day.

And then there's matter of abortion and the role of protecting reproductive rights in solidifying Obama's support among former Hillary Clinton backers. A devout Catholic (he served as a missionary in the Honduras), Kaine is personally opposed to abortion and backed so-called partial birth abortion legislation. But while his policy of supporting existing laws on abortion, as with the death penalty, has placated many Democrats, it also creates confusion.

Today, for example, the University of Virginia's Larry Sabato deemed Kaine "is pro-choice in effect while projecting a pro-life image." But last month, University of Richmond political scientist Dan Palazzolo concluded, "he's pro-life, basically." It's no wonder Kaine gets little credit on the issue from some Catholic groups.

The danger for Obama is that Kaine would get even less credit from Hillary's supporters. While the polling data show Obama has come a long way in consolidating his standing among women voters in general and Clinton's backers in particular, John McCain's anti-choice views have played a key role. Bypassing Hillary Clinton as his running mate for Kaine could reopen that wound.

None of this is to suggest that Governor Tim Kaine isn't a solid candidate and a rising star in the Democratic Party. He is both of those things. But Kaine is not the right fit for what Barack Obama and the Democratic Party need now in their vice presidential choice.