President Trump has played a starring role throughout the race for governor of New Jersey, thanks to his stronger-than-expected showing last November in the Democrat-led state. But his influence on the Republican and Democratic primaries, set for Tuesday, was impossible to miss this week.

On Monday night, just hours before the start of early voting, Trump held a dial-in telephone rally for the candidate he endorsed last month, a Republican former assemblyman named Jack Ciattarelli, who is making his third run for governor. Ciattarelli was at the front of a five-candidate G.O.P. pack long before he earned Trump’s backing.

Still, if Ciattarelli wins Tuesday’s primary and beats the Democratic nominee in November, the president will rightly be able to claim some credit.

Only New Jersey and Virginia are holding races for governor this year, and the contests will offer an early gauge of voter attitudes toward Trump, five months into his second term as president. He seemed to allude to that looming scorecard on the call, reminding listeners that the race was “being watched, actually, all over the world.”

“New Jersey’s ready to pop out of that blue horror show,” he said, making clear his ultimate goal: turning the blue state red.

The six Democrats running for governor have also placed Trump at the center of their campaigns, emphasizing how they would fight him from the Statehouse as voters have grown hungry for a more forceful response to his divisive policies. Representative Mikie Sherrill, the front-runner, has used her platform in the House to decry Trump’s policy moves. One candidate, Representative Josh Gottheimer, went so far as to step shirtless into a boxing ring and throw punches at Trump in a TV ad his campaign said it had created using artificial intelligence.