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Donald Trump.
Polls show the real-estate mogul holds a 13-point lead in Arizona, the largest remaining winner-take-all state, which holds its primary Tuesday.
He also he finds himself with double-digit polling average leads in New York and California, as well.
Those three states award the most remaining pledged delegates of any states left to vote through the rest of the primary season.
And Pennsylvania - where Trump also holds a double-digit lead - has 71 delegates, but just 17 are pledged. The remaining 54 will be able to vote for whomever they want during this summer's convention. But the unbound delegates delegates will be elected by Pennsylvania Republican primary voters - who, should they vote for Trump, might align with delegates they believe will do the same. Those delegates are elected on a county-by-county basis.
Tuesday's GOP contests in Arizona and Utah mark the start of a long slog that anti-Trump segments of the party hope will deny him the nomination outright heading into this summer's convention. Last weekend, The New York Times reported on 100-day, last-ditch effort to stop the mogul.
Even with strong showings in the four big states left on the map, Trump could still fall just short of the necessary 1,237 delegates needed to secure the GOP nomination. The data-journalism website FiveThirtyEight projected that, even with Trump winning winner-take-all Arizona and New Jersey, in addition to a majority of delegates in New York and California, he will fall less than 30 delegates short of the guaranteed nomination.
A state the so-called Never Trump movement believes is key to ensuring that Trump doesn't hit that 1,237 mark is Wisconsin, the only state holding a Republican primary between Arizona on Tuesday and New York on April 18. Utah, the other state that votes Tuesday, is also expected to be fertile ground for Sen. Ted Cruz, Trump's top remaining GOP rival.