Just as he’s regaining momentum after his big New York win, Donald Trump faces a Pennsylvania primary on Tuesday that could knock him off stride in a big way due to the state’s “free agent” delegates.

Consider this: Pennsylvania, with the seventh-most GOP delegates of any state, ranks 49th in pledged delegates. It’s behind even Puerto Rico and the District of Columbia.

Pennsylvania’s 54 unpledged delegates can do as they please when get to the national convention in Cleveland. That’s because the state has a two-tiered primary: a beauty contest that awards 17 delegates based on who receives the most votes statewide at the ballot box; and the 54 unbound delegates chosen by voters in the 18 congressional districts, with no assurances of anything.

As a result, though Trump has a big lead in the Pennsylvania polls over Ted Cruz, he may secure only a small number of delegates. And those 54 delegates who are up for grabs from now until the July convention in Cleveland could be enough to prevent Trump from securing the 1,237-delegate majority he needs to avoid a contested convention.

Here’s how the New York Times describes the Keystone State’s “loophole primary”:

… Voters (in each district) directly elect delegates to the national convention. What makes Pennsylvania’s GOP delegate selection primary so distinctive is that the ballot includes no guidance on whom a delegate will support at the national convention. … A voter will just see a list of names — some of whom might be recognizable, but others might as well be Joe Schmo.

It’s called a  loophole primary because it could circumvent the delegate allocation rules and divert sharply from the requirements in nearly every other state that say delegates must vote for their pledged candidate in the first round of convention voting.

As NBC News points out, these “free agent” delegates in Pennsylvania present a great opportunity for the Cruz or John Kasich campaigns to woo delegates regardless of the election outcome on Thursday.

In fact, the Cruz campaign already is pushing a slate of Cruz-loyalists for 26 of the 54 unbound slots up for the taking, according to NBC. Others eligible on the ballot to become delegates, particularly longtime state activists able to win on their name alone, supposedly have committed to Cruz as well. Cruz has personally met with several of the potential delegates.