WASHINGTON (AP) – Despite Donald Trump’s string of victories on Tuesday, he has to do better in upcoming contests to claim the Republican nomination for president before the party’s national convention this summer, an AP delegate count shows.

Ted Cruz is emerging as the candidate who could stop him – with a little help from Marco Rubio.

A close look at the delegate math illustrates Trump’s problem. So far Trump has won only 46 percent of the delegates that have been awarded, even though he has won 10 of the first 15 contests. It takes an outright majority of delegates to win the nomination.

Going forward, Trump would have to win 52 percent of the remaining delegates to claim the nomination. That’s doable but difficult with three or more candidates claiming delegates.

On Tuesday, Cruz muted Trump’s delegate gains by winning delegate-rich Texas, which is Cruz’s home state.

The delegate math shows the importance of the March 15 primaries in Florida and Ohio, in which the statewide winner gets all the delegates. Winning those states could boost Trump to a commanding lead in the delegate count, but Florida is Rubio’s home state and Ohio is home for John Kasich, the state’s governor.