Joe Biden campaigns for a blue-collar Democratic resurgence in Pennsylvania

In doing so Tuesday, the former Vice President offered a glimpse of how he'd approach 2020 if he runs for president again: by working to rebuild a Democratic coalition that includes white, rural, blue-collar voters. 

That approach starts in districts like Pennsylvania's 18th, where there is currently a closely watched contest taking place between Lamb and Republican state Rep. Rick Saccone, who is backed by President Donald Trump. The district votes heavily Republican; Trump beat Hillary Clinton here by 20 points in 2016. But there are actually more voters registered as a Democrats. 

"The suburbs, the exurbs, the smaller towns -- they got hit pretty hard," Biden said Tuesday at Robert Morris University, where he led a get-out-the-vote rally. 

He said Republicans "talk about caring about" and offering solutions for those regions, "but they're not doing any of it." 

"This is all within our wheelhouse," Biden said. "We've got to remember who the hell we are."

At a union carpenters' apprenticeship shop, Biden tied his earliest days in politics to local union support. "You've always had my back," he said. 

He cast Lamb, the 33-year-old Marine veteran and prosecutor, as cut from the same cloth. "He reminds me of my son Beau," the former Delaware attorney general and rising Democratic star who died of brain cancer in 2015, Biden said. 

Twice, Lamb introduced Biden as "a leader that everybody likes." There's truth to the phrase: Biden has stepped in as Democrats' most valuable surrogate in Republican-leaning and working-class regions. 

He drew a massive crowd last fall in Birmingham, Alabama, to kick off Doug Jones' push to the Senate special election. He's sought-after by Democrats in red states, with fundraising events coming up this month in Montana and South Dakota, where Democratic senators face tough re-election battles. 

Biden positioning himself as a cross-party healer is far from a unanimous position within a party that is hungry for anti-Trump brawlers and with a field of potential candidates 2020 that includes a progressive set of ambitious lawmakers.

There's evidence to support Biden's assertion that Lamb can win. Recent polls have shown a tight race, including one from Monmouth University in mid-February that had Saccone leading by just 3 percentage points.

Republicans have raced to save the deep-red district vacated when former Rep. Tim Murphy stepped down, in part because of what Biden predicted to reporters on a ropeline after his event at the union apprenticeship shop: A loss here would throw the GOP into panic and could trigger a wave of retirements. 

The National Republican Congressional Committee on Tuesday invested another $619,000 in TV ads, upping the party committee's spending to $3.5 million in the race and total GOP outside group spending to about $10 million. That's a massive price tag for a race Democratic groups are largely ignoring. 

Trump's announcement of tariffs on imports of steel and aluminum was also seen by some as a move designed to bolster Saccone's chances. Trump has already visited the district once during the special election and plans another trip Saturday. 

The steel tariffs were backed by both candidates in a Saturday debate. "For too long China has been making cheap steel, and they've been flooding the market with it. It's not fair, and it's not right. So I think it's long overdue," Lamb said then. 

Saccone used the opening to heap praise on Trump. "It's the first volley in what he's doing. He's a negotiator. He's a master negotiator. You put out the line and maybe there'll be a little bit of give and take on it, but at the end, you come out with a good deal for America," he said. 

But Lamb has been able to parry other GOP attacks. 

Republican groups had long sought to use the party's tax bill against Lamb and had also spent millions tying him to House Democratic leader Nancy Pelosi, even though Lamb has said he does not support Pelosi and would not vote for her for speaker. 

In recent days, Republicans have shifted their emphasis away from those attacks, an indicator they weren't having the desired impact, and toward attacks on his time as a federal prosecutor. 

Biden, meanwhile, swung back on the tax bill, saying it would lead to cuts in Medicare and Social Security. Of House Speaker Paul Ryan, Biden said, "If you met him, you'd think he's a decent (guy) -- he's just read too much Ayn Rand." 

"Take a look what's happening," Biden said of the GOP in the Trump era. "People are realizing the bill of goods they've been sold."