Vermont Sen. Bernie Sanders will announce his plans to seek the Democratic nomination for president on Thursday, presenting a liberal challenge to Hillary Rodham Clinton.

Sanders, an independent who describes himself as a “democratic socialist,” will follow a formal statement with a major campaign kickoff in his home state in several weeks. Two people familiar with his announcement spoke to The Associated Press under condition of anonymity to describe internal planning.

Sanders will become the second major Democrat in the race, joining Clinton. He has urged the former secretary of state to speak out strongly about issues related to income inequality and climate change. The former first lady and New York senator is viewed as a heavy favorite in the Democratic primary and formally entered the race earlier this month.

Sanders plans were first reported Tuesday by Vermont Public Radio.

The white-haired senator and former mayor of Burlington, Vermont, has been a liberal firebrand, blasting the concentration of wealth in America and assailing a “billionaire class” that he says has taken over politics.

In recent weeks, Sanders has been a forceful critic of the proposed Trans-Pacific Partnership trade agreement, which would eliminate tariffs and other trade barriers for the U.S., Canada and Asian countries conducting commerce with each other.

“One of the key reasons why the middle class in America continues to decline and the gap between the very rich and everyone else is growing wider is because of disastrous trade agreements which have sent millions of decent-paying jobs to China and other low-wage countries,” Sanders said.

He has called for universal health care, a massive infrastructure jobs and building program and a more progressive tax structure.

(AP)