BOSTON (AP) — The Republican senator who suddenly sits at the center of the explosive debate over President Donald Trump's Supreme Court pick was set to address New Hampshire voters on Monday ahead of a possible run for president.

Arizona Sen. Jeff Flake was scheduled to speak in New Hampshire Monday evening, his second appearance this year in the state that hosts the nation's first presidential primary election.

Three days earlier, Flake single-handedly delayed Brett Kavanaugh's confirmation proceedings by insisting on an FBI investigation as a condition for his support.

Flake told CBS' "60 Minutes" on Sunday that he believed the woman accusing Kavanaugh of sexual assault and said the conservative judge's nomination would be "over" if federal investigators determine he lied to the committee.

Flake, a 55-year-old lifelong conservative who is retiring from the Senate at the end of the year, has quickly emerged as the centerpiece of a passionate lobbying effort from the right and left.

Organizers said a separate Flake appearance in Boston earlier in the day was moved to City Hall after security concerns emerged about the original location.

Hundreds of liberal protesters, victims of sexual assault among them, pleaded with Flake to block Kavanaugh's nomination outside the venue. A similar demonstration was planned for New Hampshire.

New York congressional candidate Alexandra Ocasio-Cortez warned Flake and other elected leaders that voters would end their careers should they support Trump's Supreme Court nominee.

"We are going to keep pushing because justice in America is not just about protecting the powerful," Ocasio-Cortez charged. "It is about uplifting the voices that have been victimized."

Boston Mayor Marty Walsh offered a direct message to the Republican senator from Arizona.

"I guess I want to say, 'Thank you,'" Walsh said. "But that's your job. That's your job to vet the nominee."

The true test for Flake would come once the full Senate votes on the Kavanaugh nomination in the coming days, Walsh said.

"He has an opportunity to do something very special at some point next week," the mayor said.

Flake was set to address New Hampshire voters later in the day.

In March, Flake told New Hampshire Republicans that someone needs to stop Trump in the 2020 presidential contest. Flake said he may run — either as a Republican or an independent — if no one else does.

"It has not been in my plans to run for president, but I have not ruled it out," Flake said at the time.

"I hope that someone does run in the Republican primary, somebody to challenge the president," Flake said. "I think that the Republicans want to be reminded what it means to be a traditional, decent Republican."