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Donald Trump suffered a sharp drop in CNN’s Political Prediction Market after Saturday’s voting. CNN’s market uses polling and forecasts from more than 100,000 users to predict election outcomes. Trump had a 78 percent chance of winning the GOP nomination before the voting in four states on Saturday. Afterwards, in the wake of his losses in Kansas and Maine, his odds fell to 63 percent. Trump narrowly won Kentucky and tied Ted Cruz for delegates in Louisiana.

Whether or not Donald Trump becomes the GOP presidential nominee will depend in large part on whether his support is declining in strength — as it did on Saturday – or continuing to expand.

If he takes from candidates who have left the race, such as Ben Carson, he is on track to win. If he is declining, he is unlikely to enter the Cleveland convention with the 1,237 delegates needed to win, because many of the delegates bound to win on the first ballot aren’t personal supporters and will probably abandon him. Trump could cut a deal for the delegates of, say, John Kasich, who has been noticeably reluctant to criticize Trump, even in the wake of the KKK brouhaha. But there are obstacle to such a deal as well.

So far, there are signs that Trump’s debate antics, his flip-flops, and the consolidation of the GOP field is slowing him down. As Henry Enten of FiveThirtyEight pointed out, Trump won 35 percent of the vote in Super Tuesday primaries on March 1 and only 33 percent in Saturday’s contests in Maine, Kansas, Louisiana, and Kentucky. He was favored to win the first two states but saw Ted Cruz beat him instead.

Consider what happened in Louisiana, a state where Trump’s final lead in the average of all polls surveyed by RealClearPolitics was 15.6 percent of the vote. He wound up winning by three points, only because he carried early votes with 47 percent. Ted Cruz won 23 percent, and Marco Rubio won 20 percent. Of the votes cast on Election Day, Cruz beat Trump, by 40.9 percent to 40.5 percent.

Right now, Trump has won 44 percent of the delegates selected so far. Cruz has won 34 percent, and Rubio has won 17 percent. Starting on March 15, the first states to allocate delegates on a winner-take-all basis start voting, led by John Kasich’s home state of Ohio and Marco Rubio’s home state of Florida.

If Trump wins both, he will have about half the delegates needed to clinch the GOP nomination. He then would have to win just over 50 percent of the delegates selected after March 15 to reach the magic delegate number of 1,237. If he did so, he would enter the convention with enough votes for a first-ballot victory, although some of his delegates who are established party officials and not Trump partisans could abstain and bring his total below a majority.

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But, as NBC’s First Read blog has reported, if Trump wins Florida but loses Ohio to Kasich, he will then have to win 57 percent of the remaining delegates to win on the first ballot.

But if Rubio wins Florida and Kasich wins Ohio, Trump will still lead in overall delegates but would then need to win 66 percent percent of the remaining delegates to reach 1,237. Given how much of the party opposes Trump, that would be unlikely.

John Hinderaker, of the Powerline blog, acknowledged recently that while anti-Trump forces would be pleased to prevent Trump from achieving a first-ballot victory, such a strategy would carry real risks with it:

A scenario in which Trump goes into the convention as the leader in delegates but is blocked because the competition coalesces around another candidate is hardly ideal. It could result in Trump running as a third-party candidate or, at minimum, many of his backers staying home in November.

But for the anti-Trump forces, those would be manageable problems compared with having Trump himself as the nominee. A barrage of liberal attack ads, his failure to release his tax returns, his inability to hold consistent views on issues, and his sky-high negatives with independent voters would probably doom him against even the ethically challenged Hillary Clinton. In the RealClearPolitics average of all polls, Trump trails Clinton by 3.4 points, while Ted Cruz beats her by 1.5 points and Marco Rubio beats her by 5.0 points.

The key to a Republican win in the 2016 election might be to persuade the voters of Ohio and Florida to let the nomination contest play out until the Cleveland convention. At the convention, if Trump is a clear front-runner in terms of delegates, he will probably be the nominee. But if he commits more unforced errors over the next four months and displays even less discipline on the campaign trail than he has to date, Republicans will be grateful that they had the extra time to size up just what kind of nominee Donald Trump would be.

— John Fund is NRO’s national-affairs correspondent.