Democratic U.S. Sen. Elizabeth Warren said Friday she will run for a second term in 2018, signaling again that she plans to be one of her party's fiercest critics of Donald Trump and the Republican-led Congress.

Warren made the announcement - which had been expected - in a message to supporters.

"This isn't the fight we were expecting to fight," Warren wrote. "But this is the fight that's in front of us. And the people of Massachusetts didn't send me to Washington to roll over and play dead while Donald Trump and his team of billionaires, bigots and Wall Street bankers crush the working people of our Commonwealth and this country."

Warren, a former Harvard Law School professor, won the Senate seat in 2012 by beating incumbent Republican Sen. Scott Brown in her first political contest.

Potential GOP opponents in 2018 include former Boston Red Sox pitching star Curt Schilling, a strong Trump backer.