By Mark Willen, Senior Political Editor August 15, 2008 It's been clear for months that Barack Obama wasn't seriously considering picking Hillary Clinton to be his vice presidential running mate. There are plenty of good reasons for that -- the rivalry, the lingering bitterness, the problem of controlling Bill and the idea of putting a black and a woman on the same ticket. But I can't help but think the benefits outweigh the negatives.I'm not saying Obama will choose Clinton; I don't think it's in the cards. But I do think no one would help him win the election more. I must admit I had my doubts when my colleague Doug Harbrecht made that argument two months ago, but a lot has changed since then, all of it reinforcing Doug's argument. Obama has had a rough couple of months. Though he still leads in most polls, it's a small, tentative lead and McCain's negative attacks are taking a toll. Now there a new bestseller spreading slurs about Obama's history and several reports of dirty trick campaigns. In some southern states, white voters in rural areas have been getting calls from people claiming to be supporters of Obama, but they are clearly trying to undercut him. The callers sound black, have rap music playing in the background and say Obama would be a good president because he'd use the full force of the White House to the benefit of African-Americans. This message, the opposite of what Obama has said, is clearly designed to arouse racial fear. Obama is going to need a real attack dog as a running mate. Other candidates -- notably Joe Biden -- can play that role, but nobody can do it better than Hillary and Bill, and Obama could use their political smarts on his side, rather than have them sit on the sidelines, giving only half-hearted support. Plus, the ticket would unify the Democratic Party behind Obama, a goal that remains elusive. And it would sure help boost the turnout among women for Obama. Advertisement As active campaigners, the Clintons could help in several swing states with white middle class voters who now hesitate to support Obama -- including Pennsylvania, Ohio and Michigan. And they'd be all over McCain in a way that would allow Obama to stand above the fray. While his advertisements this week have become increasingly negative, he risks losing his image as a different kind of politician if he adopts too negative a tone. It once seemed that putting Hillary on the ticket would hurt by mobilizing the Republican base, helping McCain get his supporters to the polls. But it's now clear that the right is already rallied against Obama, so there is less to lose by picking Hillary. There are also concerns about Bill's financial dealings since leaving the White House, but given the lack of public interest in McCain's lobbying ties, it's hard to see voters getting too exercised about the connections of the spouse, albeit an unusually important one, of the vice presidential candidate. Again, we still don't think an Obama-Clinton ticket is in the cards, but Obama strategists might do the candidate a favor by reconsidering it. And it's not too late.