WASHINGTON — So far, so good for Joe Biden.

As he returns to Philadelphia for a rally Saturday at Eakins Oval, the former vice president will cap his initial burst of campaigning with unquestioned momentum. In his three weeks in the race for the Democratic presidential nomination, he has expanded his lead in national polls and is running far ahead of the pack in key early states as well as in Pennsylvania, leaving his rivals scrambling to react to his cannonball entry into the campaign.

In his 1 p.m. rally, Biden plans to more fully lay out the third and final “pillar” of his campaign, a call to unify the country and counteract President Donald Trump’s divisive tenure.

Then comes the next tests: weathering the attacks that come with being the front-runner, laying out a policy platform, and defending a long public record now that he has become the focal point of a kaleidoscopic field.

Trump, his campaign, and other Democrats have started singling out Biden, predicting they can dent his standing once he comes under new scrutiny.

“When you look at Joe Biden, he has a very poor record” that “he hasn’t been confronted with yet,” said Kayleigh McEnany, Trump’s national press secretary. “I fully expect he will be.”

Biden seems to welcome the president’s attention as he seeks to portray himself as the Democrat with the time-tested stature to take on Trump.

>> READ MORE: Joe Biden 2020: How he could win. And why he might not.

Biden’s familiarity, after eight years as vice president to Barack Obama and nearly 50 years in public life, is the strength that his allies say has made him the early leader in the sprawling primary.

“Put this in parentheses, capitalize it, put it in red: trust. They trust him,” said Bob Brady, chairman of the Philadelphia Democratic Party and a Biden supporter.

Joe Biden takes a selfie with a supporter during a campaign stop at the Community Oven restaurant in Hampton, N.H., on Monday.
Michael Dwyer / AP
Joe Biden takes a selfie with a supporter during a campaign stop at the Community Oven restaurant in Hampton, N.H., on Monday.

Kenneth Glover, chairman of the Democratic Party in Orangeburg County, S.C., also pointed to Biden’s long history in explaining why the former vice president has dominated early polls in the state, winning support from 46 percent of likely Democratic primary voters, up 14 percent from last month, according to a Charleston Post and Courier-Change Research survey released Sunday.

“He’s always been popular among Democrats here, especially in the African American community,” said Glover, who has not endorsed in the race. “It doesn’t hurt that he was vice president to President Obama.”

In Pennsylvania, the state Biden has made central to his strategy and where he plans to base his campaign, the former vice president now tops the Democratic field with 39 percent support within his party, triple that of his closest rival, Sen. Bernie Sanders (Ind., Vt.), according to a Quinnipiac University poll released Wednesday.

About 61 percent of Democrats named Biden as the contender with the best chance to defeat Trump — a sentiment shared by liberals, moderates, and conservatives, said Mary Snow, a Quinnipiac analyst.

With Biden rising, rivals have scrambled to recalibrate their campaigns and pull him back into the pack. Trump plans a rally Monday near Williamsport. Ostensibly it’s to boost a fellow Republican in a congressional special election, but there are no signs that race is close.

Biden’s long career also has opened him to attacks, which have begun pouring in as he has capitalized on an initial jolt.

“I voted against it. Joe voted for it.”
Sen. Bernie Sanders (I., Vt.), on the Iraq War

“Maybe the most significant vote that members of Congress have taken in recent years was on the war in Iraq,” Sanders said at a town hall event in Iowa this month. “I voted against it, Joe voted for it.”

He and other Democrats, as well as the Trump campaign, also have targeted Biden’s support for international trade deals such as NAFTA and the scuttled Trans-Pacific Partnership, trying to undercut his appeal to blue-collar workers, who largely loathe such agreements, and blaming him for lost manufacturing jobs.

Biden stood by his NAFTA vote this week, telling the Associated Press: “Fair trade is important. Not free trade. Fair trade. And I think that back in the time during the Clinton administration, it made sense at the moment.”

When Biden said Tuesday that Republicans would have an “epiphany” and grow more reasonable if Trump was defeated, some liberals seized on the comment as evidence that his back-slapping methods don’t fit today’s politics.

“In this outsider moment, Joe Biden is the consummate political insider who loves to cut backroom deals with big corporations and corrupt Republican politicians,” said Adam Green, co-founder of the Progressive Change Campaign Committee, which is supporting Sen. Elizabeth Warren (D., Mass.).

Green argued that Biden is riding an “electability bubble,” fueled by perception, that can be punctured once people focus on his policies.

Sen. Kamala Harris (D., Calif.), a former prosecutor, blasted Biden’s support for a 1994 crime bill, telling reporters in New Hampshire on Wednesday that “it did contribute to mass incarceration.”

Democratic presidential candidate Sen. Kamala Harris (D, Calif.) speaks at a Service Employees International Union forum on labor issues last month in Las Vegas.
John Locher / AP
Democratic presidential candidate Sen. Kamala Harris (D, Calif.) speaks at a Service Employees International Union forum on labor issues last month in Las Vegas.

Biden has avoided responding to the criticism, campaigning like an incumbent loath to offer fuel to lesser-known rivals.

Press access has been tightly controlled compared with other candidates, helping Biden avoid the verbal gaffes that sometimes have tripped him up. His team sends out daily press guidance even when he has no public events, much as the White House does for presidents. He has toured all four early voting primary states, held major fund-raisers, with pool reports from each, and swung by a pizzeria, an ice cream shop, and a taco stand on his travels.

Allies say his early success shows that the actual Democratic electorate is less focused on aggressive liberal policy than Twitter might indicate, and that he is well-established enough to withstand the attacks. A Politico/Morning Consult poll released last week found that only 9 percent of Democrats said Biden’s NAFTA vote, for example, would make them less likely to support him, although the Iraq issue appeared to be a more potent line of attack.

“Voters know Joe Biden,” said T.J. Ducklo, a Biden spokesman. “They know his values and they know his character. They also know Joe Biden doesn’t just speak out on progressive causes, he takes action.”

Ducklo cited as examples Biden’s efforts to promote infrastructure and clean energy investments, and his work on rescuing the economy while he was vice president.

After the rally Saturday, Biden is expected to turn to rolling out policy details, which could provide fresh fodder for his rivals and test whether his vision fits the party’s mood.

The Quinnipiac Poll found that 23 percent of Democrats believe Biden has the best policy ideas, a relatively narrow edge over liberals Sanders and Warren, who each garnered 18 percent.

In late June, Biden will argue alongside his rivals when Democrats hold their first primary debates, potentially an early inflection point for the crowded field.

While Biden has momentum, his competitors have room to grow, said Jesse Ferguson, a Democratic strategist who worked on Hillary Clinton’s 2016 campaign.

“The one thing that’s known about this primary is that there’s a lot that’s unknown,” Ferguson said. “It started earlier than ever before, it’s going to run longer than ever before, and there are more candidates than ever before.”