Strictly by the numbers, Mitt Romney's narrow victory last night in his home state of Michigan was modest. He won only 3 percent more votes than second-place finisher Rick Santorum and, because the primary is not winner take all, the two candidates will split the real prize -- Republican delegates -- nearly equally.

In his victory speech, however, Romney was clearly more concerned with the symbolic victory. "We didn't win by a lot, but we won by enough, and that's all that counts," he told supporters in Novi, Mich. While it's unlikely Romney was watching the prediction markets as closely as we do before he took the stage, he would be pleased to know that they agree. Within an hour of Michigan's outcome becoming clear, Romney's likelihood of earning the Republican party nomination jumped to 80.9 percent, up 8.3 percent from Tuesday evening. (No one likes a gloater, but we did call that.)

Some commentators still question whether Romney's win in Michigan gives him sufficient momentum

Update, 9:49 p.m. ET: Mitt Romney is now very likely to carry the state of Michigan. With 50% of the state reporting he is up by almost 20,000 votes to Rick Santorum and we project him as 96.9 percent likely to hold that lead to victory.

The markets reacted quickly tonight allowing The Signal to be among the first news sites to signal Romney's likely victory (follow us on Twitter for the fastest reaction pieces during breaking news events):

Likelihood of Winning Michigan Primary

The Signal has favored Romney as the likely winner throughout the time between his big losses on February 7 and when the polls closed tonight the likely victory marks an important milestone on his road to his likely Republican nomination. As projected, he has increased his likelihood of gaining the Republican nomination by nearly 6 percentage points since the polls closed from 72.8 percent to 78.5 percent.

Ahead of tonight's primary results, we see two possible paths the prediction markets could take depending on what happens in Michigan.

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The longer-than-expected Republican primary has given many more voters a chance to meet the candidates and cast ballots in meaningful elections, but it has caused some in the party to worry that it is weakening the eventual winner in his confrontation with President Obama. Mitt Romney is still the heavy favorite to win the nomination, with 75.2 percent odds to Rick Santorum's 9.8 percent, but the data suggests he could be looking at a Pyrrhic victory. The president's odds of re-election jumped to above 60 percent in the days after Santorum's big wins on February 7, according to prediction markets. Since then they have steadily crept up; by contrast, Obama spent the fall and early winter hovering around 50 percent.

We can compute the Republican challengers' likelihood of victory against Obama, should they win the Republican primary, by dividing their likelihood of becoming president by their likelihood of winning the nomination. Because this is a "conditional probability" -- you can