Short answer: probably not much, as far as the final outcome goes, though it does allow Hillary to drag things out a little longer, if she wants.
Checking out what's still yet to report in Ohio, it appears as though much of it is Cuyahoga county, which is only currently listed at 44%. If current voting trends there stay on track, this should mean about another 9K Obama votes and about a 54%-43% win for Clinton. That 11% margin is basically what Quinnipiac predicted on the 23rd of February.
In one sense, all the negative campaigning by Clinton appears to have hurt Obama, but it looks like it only had a strong impact amongst voters who traditionally would trend towards Hillary. It certainly didn't work -- and may have backfired -- in Vermont, where Obama racked up the largest margin victory of the night. Such tactics tend to take advantage of preconceived biases.
So, will Obama be weakened elsewhere too? My guess is that it won't in Wyoming and Mississippi, but could have an effect in Pennsylvania, somewhat along the lines that it might've had in Texas. (i.e. minor.)
Although Obama narrowly lost the Texas popular vote, it looks like Obama is going to win the majority of Texas's delegates. He's done almost exactly as predicted for the delegates in the primary -- basically a push or a slight lead, based on the lower delegate count that latino voters will have based on their low participation in 2004 -- while leading in the caucus at this time. Unfortunately, it is very hard to figure out the statistical meaning of the caucus results tonight, though it does seem to be tilting towards Obama by several percent.
Vermont and Rhode Island will each result in about a 3 delegate shift for each candidate, so Hillary's overall gain for the night is looking to be a very small gain. Talkingpointsmemo says that Clinton may gain as few as seven delegates in Ohio, and could even lose several in Texas... If there is any possible shift towards Hillary Clinton, I think it could be less than 10 delegates.
That's about the same as Obama's gain for his strong win in Wisconsin... and based on current polling, Obama will probably make up any loss with likely wins in Wyoming and Mississippi. Really, this was Hillary Clinton's big chance to close the gap, but her firewall appears to have gone up in smoke. It'll be interesting to see what the statisticians say about her chances after this. Losing badly in the next two contests could decide it, in that it would give the remaining superdelegates a good chance to call the race before it drags on for another month.
So, tactically, tonight could be called a symbolic Clinton victory, but strategically, it's a minor Obama victory. Basically, he wins by not losing traditionally blue states by large margins, while winning traditionally red states by very large margins. Meanwhile, I think we have to see what the superdelegates do. My guess is that Obama will pull even in superdelegates if he gets wins in both Wyoming and Mississippi, in part because lots of party Democrats do not want to wait until Pennsylvania, because it will financially and structurally weaken the party.
I think that Obama needs to use surrogates to go strongly negative against Hillary, clearly spelling out her record as First Lady, Travelgate, her repeated use of "I do not recall..." in testimony, her failure to turn over subpoenaed files, her well-documented White House rages and tantrums as indicated by former members of the Clinton administration, her campaign financing scandals, and doing a daily drumbeat about her tax records. By using surrogates, Obama can give reasonable sounding responses to such allegations, yet ones that leave the voter feeling doubt in Hillary Clinton's record and credibility.
I still don't think it's likely that this race will go to the convention -- Howard Dean and several people in the Democratic party establishment have made it clear that they want this thing over soon, and will intervene as a bloc to prevent things from going undecided for much longer. Expect wins in Wyoming and Mississippi to give them that chance. If she threatens to bring things to the convention, the best defense against such behavior is in damaging her credibility now, so that superdelegates start to feel that she is an an unelectable candidate.
In other words, they've "kitchen sinked" Obama, he has to be prepared to do the same to her, in order to destroy her credibility... ideally in a way that makes it clear that she has to knock off her attacks. Mutually Assured Destruction.
She needs to know that if she continues this fight, it will permanently damage her career. Fortunately, there are a lot of ways to do this.Things are about to get "interesting", I suspect. It might not be good for the party, but that appears to be the fight Hillary Clinton has chosen.