PHILADELPHIA — In two of the most pivotal Senate races in the country, Democrats are placing their bets on progressives who have voiced support for Medicare for All, allied with Bernie Sanders and vowed to end the filibuster.

In Wisconsin, Lt. Gov. Mandela Barnes gained a clear path to the nomination on Tuesday after his top Democratic rivals dropped out and endorsed him in the final weeks of the race. In Pennsylvania, Lt. Gov. John Fetterman won the primary in a rout in May.

The rise of Barnes and Fetterman is an opportunity for the left wing of the party, which has often struggled to flip swing seats and instead found success in ousting Democratic incumbents in deep-blue areas. Both men have said they would be the 51st vote to pass ambitious liberal legislation that has been stymied by centrist Sens. Joe Manchin (D-W.Va.) and Kyrsten Sinema (D-Ariz.), and both say they support eliminating the filibuster and passing a national law to make abortion legal.

“When they’re victorious, it will have such a huge impact for so many reasons,” said Maurice Mitchell, national director of the progressive Working Families Party. “Every week it becomes more and more plausible that the Democrats maintain governing majorities in both houses, and might even expand the governing majority in the Senate. That will mean that we get another bite at the apple of governing. It means that we will no longer be subject to the Sinema or the Manchin veto.”

Republicans, meanwhile, see the ascension of Barnes and Fetterman as an opening to pick off independent and suburban voters. During their primaries, many GOP operatives thought they were likely to be less formidable general election candidates than their more moderate opponents.

“Democrats nominated the most liberal candidates they could find in states that are struggling because of Joe Biden and the Democrats’ agenda that’s resulted in record gas prices, skyrocketing inflation, crime raging, and a border crisis,” said Chris Hartline, a spokesman for the National Republican Senatorial Committee. “We look forward to watching Mandela Barnes defend his embrace of defunding law enforcement and John Fetterman defend his support for banning fracking.”

Pennsylvania is widely considered to be the best chance for Democrats to flip a seat in the evenly divided Senate, while Sen. Ron Johnson in Wisconsin, Barnes’ opponent, is viewed as the most vulnerable Republican incumbent in the chamber.

The fact that Democrats are rallying behind Barnes and Fetterman represents a departure from past election cycles, when they typically selected centrist candidates to be their standard bearers in battleground Senate races. That has worried some moderates in the Democratic Party who believe the candidates have baggage that could alienate swing voters.

When Barnes touted Sanders’ endorsement last month, Matt Bennett, a co-founder of the center-left group Third Way, tweeted, “Why would you do this? WHY???”

In an interview, Bennett said that Barnes is “a very appealing candidate in many, many ways for both wings of the party. He’s dynamic and smart and young and he could be great. But we were nervous — we are nervous — that some of the things he’s done and said are going to make it tough to win in a swing state like Wisconsin.”

Senate candidate Mehmet Oz speaks at a rally at the Westmoreland County Fairgrounds on May 6, 2022 in Greensburg, Pennsylvania.