SOMERVILLE -- U.S. Sen. Bernie Sanders, I-Vermont, slammed Senate Republicans' budget plan at a Somerville rally Monday.

Under the bill, "Many thousands of people will die unnecessarily every single year in order to give tax breaks to billionaires," Sanders said.

The U.S. Senate passed a budget bill Thursday, 51-49, with all Democrats and Republican Rand Paul, D-Kentucky, voting against it. The budget bill is a precursor to the introduction of a tax reform bill.

Sanders is a progressive whose Democratic presidential bid galvanized a national progressive moment before he lost the party's nomination to Hillary Clinton.

Sanders spoke in the liberal bastion of Somerville-Cambridge at ONCE Somerville, a local event space, to endorse 18 candidates for Somerville alderman and school committee and Cambridge city council.

Sanders criticized the Senate Republican tax plan for including $1.9 trillion in tax cuts, with "80 percent of them going to the top 1 percent." He said the plan would make massive cuts to Medicaid, "throwing 15 million people off health insurance."

Sanders' presidential campaign was primarily focused on issues related to income inequality. He is continuing to press that theme, criticizing Republicans who now control the White House, U.S. Senate and U.S. House for favoring the wealthy. "What you're looking at is the evolution of this country into an oligarchic form of society where public policy is not determined by and for the people but by and for the oligarchs," Sanders said.

After losing the election, Sanders formed a political action committee, Our Revolution, aimed at supporting local progressive candidates.

Sanders used his speech to stress the importance of grassroots activism and of working people running for office. "Throughout the history of the country, fundamental change has never taken place when president signs a bill or someone on top makes a decision," Sanders said. "It's always taken place as result of grassroots activism and millions of people who looked around and said the status quo is not satisfactory, we need to move in a new direction."

A group of Cambridge Democratic activists, including State Rep. Marjorie Decker, D-Cambridge, wrote to Sanders criticizing his decision to endorse six of 26 candidates in the Cambridge City Council race. The group includes supporters of Sanders and of Clinton, and of some of the local candidates Sanders endorsed.

The group wrote that most of the Cambridge candidates are equally progressive, and differ mainly in personal background and local issues. "Intervening in the Cambridge city council race is a counterproductive choice and divides, rather than unites, progressives here," the activists wrote.

They wrote that the process Our Revolution uses to endorse candidates was "not transparent and open."

"All of us are concerned that the candidates were chosen without regard to whether they differ on the economic and social justice principles that are your platform," they wrote. They wrote that the endorsement effectively has Sanders aligning with one side of a debate over how to deal with the need to build housing in Greater Boston.

In his speech, Sanders spent little time discussing the candidates themselves, and he did not mention them by name. Rather, he focused on promoting the policies that drove his presidential campaign: raising the minimum wage to $15 an hour, providing universal single-payer health care, building affordable housing, offering free public college, reforming the criminal justice system to jail fewer people, and providing a path toward citizenship for immigrants who entered the country illegally.

Sanders said the job of his supporters is to tell President Donald Trump, a Republican, "that he will not be successful in dividing this country up based on our religion, based on our sexual orientation, or the color of our skin, or the country that we were born in."

Sanders supporters had one major state-level victory last week when Paul Feeney, Sanders' 2016 Massachusetts state director, won a special election to the state senate from Bristol and Norfolk counties.

Feeney recalled a supporter who told him on Election Day that Feeney got his vote because "you're a Bernie guy."

Several rally attendees said they would be more likely to vote for a local candidate who had Sanders' support. "I don't know that much about the Somerville candidates, and I trust Bernie," said Jim Miller, 71, a retired engineer from Somerville.