PITTSBURGH -- Jon Price was not old enough to vote in 2016, but is keeping a close eye on the expansive field of 2020 Democratic presidential candidates. He likes Kamala Harris, Elizabeth Warren, Pete Buttigieg and Bernie Sanders.

The 20-year-old says it's "way too early" for him to make up his mind. But as he waited for Sanders to speak at a recent rally in Pittsburgh, Price was weighing which candidate might be best positioned to defeat U.S. President Donald Trump.

Sanders, the Vermont senator, democratic socialist and liberal icon, "has the potential" to come out on top, Price said.

That "potential" is at the forefront of Sanders' campaign. He's coming off a swing through the Midwest in which he made the case that his proposals to raise taxes on the wealthy , provide "Medicare for All" and make public college tuition free aren't too liberal for Rust Belt voters who swung to Trump in 2016 after backing Democrats for decades.

It's precisely this platform, the senator would argue, that can win back voters from Pennsylvania to Wisconsin and deny the president another four years in the White House.

The electability question surrounding Sanders' second White House bid will come into greater focus in the coming weeks. Former Vice-President Joe Biden, who has blasted Democrats recently for embracing socialism, is expected to soon launch a campaign that also makes an explicit play for the Midwest, but with a more centrist message.

Not to be outdone, Trump is putting a priority on keeping the states he wrested from Democrats. Following a recent campaign event in Michigan, the president will hold a campaign rally later this month in Wisconsin.

his prediction on Tuesday that Sanders and Biden would be the final two candidates in the Democratic primary and said he looks "forward to facing whoever it may be."

Sanders is emerging as the early Democratic front-runner, raising more money than any of his rivals in the first quarter and taking risks that other contenders have eschewed. That was especially true with his decision to participate in a Pennsylvania town hall meeting hosted by Fox News, a network unpopular with some Democrats.

"Why would you even agree to do that?" Sanders campaign manager Faiz Shakir said of the town hall in a recent interview. "The reason is that we are thinking about electability and talking to all audiences, including audiences that we may need to convince in the general election to start making out the case against Donald Trump and laying out the contrasts."

Sanders underscored that point during his Midwest rallies by repeatedly making a general election argument reassuring those who worry his liberalism would hand Trump a second term.

"We are not going to let him win them in 2020," Sanders bellowed in Pittsburgh, promising that he would deliver general election victories in Pennsylvania, Michigan and Wisconsin.

Left unsaid was the fact that Sanders lost Pennsylvania by 12 points to Hillary Clinton during the 2016 Democratic primary. Trump later won it during the general election.

In the fast-changing Philadelphia suburb of Delaware County, where Clinton won 60 per cent in the 2016 primary, Democratic Party chair Colleen Guiney said it's hard to know whether Sanders really would have beaten Trump.

"All politicians are confident in their strengths, and I'm sure that's his impression," she said. "Who knows what would have happened?"

Belinda Beal doesn't have such doubt. As the 40-year-old from Clinton Township, Michigan, waited for a Sanders' rally to begin, she recalled crying when he lost the 2016 nomination.

She said she believed his chances in 2020 are greater because people "see what has happened since. I think they'll be more dedicated to getting him in this time."

In Pennsylvania, Barbara Wank, 86, backed Clinton during the primary, believing that she was best suited to defeat Trump. She now says she believes that Sanders would have defeated Trump in her state in 2016. But, she's less certain about 2020.

"This is not that year," Wank, who lives in Lancaster, Pa., said. "So much has gone on since then, including four years that he has grown older...While I agree with him, I'm not sure he's the best candidate."

Meanwhile, Biden's candidacy looms. Like Sanders' team, Biden allies have argued that he has a unique ability to win back white, working-class voters.

Bill Kortz, a former steel worker and a seven-term state representative from outside Pittsburgh said that Biden is the only Democrat who can defeat Trump in a general election and that Sanders is "too far to the left" to appeal to moderates.

"Joe has that charisma and the ability and the relationships here in Pennsylvania to win it big," Kortz said, adding that Biden "would smoke Trump" in the state.

But in Wisconsin, Peter Rickman, a Milwaukee labour activist who led Sanders' state delegation to the 2016 Democratic National Convention, dismissed the idea that Biden would resonate with the senator's supporters as "baloney."

"Just because you put on a hard hat and tour a factory doesn't mean you know what it's like working 40 hours a week supporting a family," Rickman said.

While Biden and Sanders seem to be on an unavoidable collision course in the primary that will put their contrasts on full display, Sanders demurred Monday when asked whether Biden was a progressive.

"Joe is a friend," he said during the Fox town hall. "He will give his point of view, I give mine, let the people decide," Sanders said.