Republican presidential front-runner Donald Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE has secured more than half of the delegates needed to win the nomination, but he will need to pick up his pace to clinch 1,237 delegates and avoid a contested convention.

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Trump’s strong performance in the Tuesday night primaries will make it tough for Sen. Ted Cruz Rafael (Ted) Edward CruzSenate Republicans face tough decision on replacing Ginsburg Cruz: Trump should nominate a Supreme Court justice next week Renewed focus on Trump's Supreme Court list after Ginsburg's death MORE (R-Texas) to catch him.

He has secured 621 delegates, according to The Associated Press's projections as of 8:00 a.m. Wednesday, compared to 396 for Cruz and 138 for Ohio Gov. John Kasich.

Those three men are now the only active GOP candidates. Sen. Marco Rubio Marco Antonio RubioFlorida senators pushing to keep Daylight Savings Time during pandemic Hillicon Valley: DOJ indicts Chinese, Malaysian hackers accused of targeting over 100 organizations | GOP senators raise concerns over Oracle-TikTok deal | QAnon awareness jumps in new poll Intelligence chief says Congress will get some in-person election security briefings MORE (R-Fla.) suspended his campaign on Tuesday after losing Florida. He has 167 delegates.

About 60 percent of the 2,472 GOP delegates have been awarded, and Trump has won about 47 percent of them.

If he continues to win at that same clip, he’d fall more than 100 delegates short of 1,237, which would set up a contested convention.

That's the result Kasich is hoping for, since the Ohio governor has no chance of getting to 1,237 himself and little realistic chance of overtaking Trump.

Cruz believes he can still take the delegate lead from Trump, but he would have a better chance with Kasich out of the race and only two men to divide up the rest of the delegates.

Even that road would be tough for Cruz, however, who would need a win in Arizona's winner-take-all primary next week as well as a victory in Wisconsin's April 5 contest.

For Trump to get to 1,237, he needs to win more than about 60 percent of the remaining delegates.

But make no mistake: Tuesday was another good night for Trump.

He won at least three of the five states up for grabs on Tuesday — Florida, Illinois and North Carolina, netting at least 150 delegates. Missouri is too close to call as of early Wednesday morning.

There are still 101 delegates yet to be awarded from Tuesday. Many will go to whoever wins the Missouri primary — Trump or Cruz. A significant swath of Illinois delegates also must still be awarded by the results of congressional districts in the state.

Trump did pass a key threshold on Tuesday by winning a majority of delegates in his eighth GOP contest. Convention rules currently stipulate that only candidates who pass that threshold are eligible for the nomination.

Trump is the only candidate to reach the marker, but the threshold can be easily changed by convention delegates before the convention begins.

Rubio's decision to drop out of the race could help Trump pick up his delegate pace, as he has one less candidate to split delegates awarded proportionately by states.

While Arizona, Delaware, Nebraska, Montana and New Jersey still have winner-take-all contests, most of the remaining states do not.

Cruz's hope is that supporters of Rubio will move to his campaign.

Avik Roy, a former Rubio healthcare adviser, immediately called for “Rubio supporters—and all conservatives—to unite around [Ted Cruz]” in a post on Twitter.

His surrogates are also calling for Kasich to drop out of the race.

“If John Kasich stays in the race, he may as well contribute all the money he spends in-kind to Donald Trump, because he will make it so that Cruz cannot compete with him in the winner-take-all states,” former Cruz aide Rick Tyler said Tuesday night on MSNBC.

If Trump doesn't get to 1,237, delegates at the convention will cast ballots.

If no one reaches the 1,237 threshold on a first ballot, Trump, Cruz and Kasich can try to pick off each other’s delegates.

That makes it important for the campaigns to try to solidify loyalty among those serving as delegates at the convention.

The candidates also could make the play for the group of Rubio delegates who can be released by the candidate and will go to the convention unbound ahead of the first ballot.

State laws differ — some will be forced to stick with Rubio and others will be automatically reallocated, but a significant portion will be up-for grabs.

With Rubio out of the picture, Cruz will likely make a strong play for Utah’s 40 proportional delegates with the backing of the state’s junior senator, Mike Lee Michael (Mike) Shumway LeeMcConnell shores up GOP support for coronavirus package McConnell tries to unify GOP Davis: The Hall of Shame for GOP senators who remain silent on Donald Trump MORE.

After that, Cruz will have to look to pick off delegates in congressional districts with heavy conservative populations to offset Trump’s further gains.

Kasich told his supporters that he would head to Philadelphia after his win in Ohio, a move likely meant to shore up his support in the Northeast and Mid-Atlantic, which will hold contests toward the end of April. The Ohio governor won’t likely be able to make a serious play in any of the contests before then except for Wisconsin.

Trump also looms large in the Northeast, especially if he can repeat his blowout victory in Massachusetts earlier this month, where he won almost 50 percent of the vote. He’s also poised to do well in his home state of New York, as well as in Arizona, thanks to his harsh border control rhetoric and his endorsements from prominent conservatives in the state.

This report was updated at 8:13 a.m.