With delegate leads growing for Donald Trump and Hillary Clinton, many experts believe that the 2016 presidential primary contest may now be all but over.

On the Republican side, Donald Trump stands with 987 delegates, far ahead of his closest competitor, Texas Sen. Ted Cruz, who has 562. Hillary Clinton leads the Democratic race, holding 2,164 delegates, while Vermont Sen. Bernie Sanders trails her with 1,355.

Clinton and Trump widened their leads on April 26.

Trump swept the races for Republicans, winning all five states up for grabs–Pennsylvania, Connecticut, Rhode Island, Delaware
and Maryland.

Clinton put in a similar performance on the Democratic side, winning every state except for
Rhode Island.

With these strong performances adding to already large leads among delegates, Ed Chervenak, University of New Orleans political science professor, thinks that challengers to Clinton and  Trump no longer have a realistic shot of winning.

“For all intents and purposes, the Democratic contest is over,” Chervenak said. “And it’s the beginning of the end on the Republican side. If Donald Trump wins Indiana next week, it’s all over.”

For Democrats, 2,383 delegates are needed to secure the nomination. There are 1,246 delegates still available, meaning that Clinton only needs to win a minimum of 18 percent of the remaining delegates to secure the nomination.

Similarly for Trump, he needs to secure 250 delegates, or 43 percent, of the remaining 583 delegates to not have the Republican convention contested. In that case, the delegates would have to negotiate with one another and find a suitable nominee that wins with a majority vote among them.

Robert Mann, Louisiana State University journalism professor and former U.S. Senate press secretary, said that this scenario is becoming less likely.

“I think that Trump is coming very close to being unstoppable,” Mann said. “He’s going to arrive at the convention with either a majority of the delegates or 20, 30, 40 delegates shy of a majority, and I think it’s going to be impossible to deny him the nomination without creating a split in the party that would be just devastating to whoever eventually got the nomination if it
weren’t Trump.”

Mann also said that the race for Democrats is no longer in question, seeing Sanders cutting hundreds of staffers as clear evidence that the Vermont senator is winding down his campaign.

“It’s now a question of ‘How does he get out?’ and ‘When does he get out?’ and does he do it in a graceful way or in a way that causes division in the party,” Mann said.

Sanders’ campaign team said that he is relying on the unbound superdelegates, who currently strongly favor Clinton, to switch support to him at the convention, but Sean Cain, Loyola political science professor, said that this is not a strategy that would serve either Sanders or the Democratic party well.

“He just doesn’t have the numbers, and it would look petty,” Cain said. “But he has enough support that he will ask for a major presence at the convention.”

On the Republican side, the only candidate that could secure the nomination before the convention is Trump, which is why Mann thinks that Cruz announced Carly Fiorina as a running mate as a last minute effort to try to deny Trump a majority heading into the convention.

“If I were Cruz I guess I’d be doing the same thing–looking for anything at all to throw roadblocks in Trump’s way and try to make it harder for him to get that majority,” Mann said.

The next state to vote will be Indiana next Tuesday, May 3.

The Republican National Convention will be held July 18-21 in Cleveland, and the Democratic National Convention will take place July 25-28 in Philadelphia.