(CNN) Joe Biden is set to shift into a new -- and riskier -- phase of his campaign for the 2020 Democratic presidential nomination.

After entering the race three weeks ago as a stronger-than-expected front-runner, the former vice president is set to deliver a speech at his first major rally of the race Saturday in Philadelphia. Then, Biden and his aides have said, he'll begin rolling out policy proposals. And, he said, he will soon likely begin preparing for the Democratic presidential debates.

It all comes with higher stakes than the small events in early-voting states like Iowa and New Hampshire that Biden has held so far, and will test his status as the front-runner, as his 2020 competitors seek to knock him off his perch and reshape the primary race.

Biden's entry has already forced other candidates to shift their own tactics and made the former vice president a target of criticism on the campaign trail.

After Biden made attacking President Donald Trump central to his campaign roll out, California Sen. Kamala Harris is now speaking much more about Trump on the trail. Former Texas Rep. Beto O'Rourke is now doing nationally televised interviews, including a CNN town hall next week in Des Moines, after months of avoiding them to focus instead on intimate campaign stops and town halls. Vermont Sen. Bernie Sanders is highlighting his contrasts on policy issues like trade and climate change with Biden.

As other candidates attempt to catch up, Biden is now moving into what his aides view as a new phase of his campaign.

Instead of focusing squarely on Trump, the coming weeks will see Biden forced to engage more forcefully in the debates driving the Democratic primary contest. He'll face more criticism from opponents, particularly if his policy proposals are not seen as sufficiently progressive. His crowd sizes will be seen as a gauge of voters' enthusiasm for his candidacy.

"This race, lot can happen. But the one thing that I know is that I don't yield anybody on my liberal credentials, whether it's on women's issues, on LGBT issues, on speech, on all those issues," Biden said Tuesday in New Hampshire.

"There are very loud voices on the very new progressive side of the agenda and I think it's useful. I think they're good. They're smart people and they should be able to be making their case," he said. "But the idea that somehow the Democratic Party has gone so far to the left that it is not recognized by most Democrats who consider themselves liberal is not factually what's happening."

After a relatively low-key start to his first swing through the early-voting states with smaller crowds and sometimes-meandering stump speeches designed to highlight his swings at Trump and minimize clashes with other Democratic contenders, Biden this week began taking questions -- both from his crowds and the reporters following him -- in New Hampshire.

Biden's strong position in the polls have placed him at the center of most Democratic debates -- and forced the other candidates to react to him.

There were moments of conflict with his competitors -- including Biden's insistence Tuesday that the 1994 crime bill "did not generate mass incarceration," which prompted Harris to fire back that Biden was wrong about the bill's effects.

Washington Gov. Jay Inslee is even pre-butting Biden's speech on climate change, which he will deliver before the end of this month -- though aides would not specify when or where.

"I was concerned, like most everyone was, of the comments coming out of this campaign," Inslee said, referring to a recent Reuters report in which a Biden adviser touted a possible approach that seeks a middle ground on climate policy. Biden's campaign has since challenged the accuracy of that report.

Referring to the Republican majority leader of the Senate, Inslee said that if Biden thinks he will "walk in and have a cup of tea with Mitch McConnell and convince him that the climate crisis demands a full mobilization of the US economy, there's some other Mitch McConnell in the world."

Biden will next grab the spotlight on Saturday in Philadelphia, with a speech at his first large rally of the 2020 race.

Saturday's speech will emphasize a theme of "choosing unity over division and making sure we have a president for all of us," a Biden aide said.

The choice of Philadelphia -- where his presidential campaign will be based -- carries both personal and political importance: The Scranton-born Biden, who represented neighboring Delaware in the Senate, is emphasizing his connection with the region. And Pennsylvania -- along with Wisconsin and Michigan -- are likely the most important states in Biden's vision of a 2020 election in which Democrats win back a share of the white, working-class voters, particularly those who backed former President Barack Obama and then voted for Trump and cemented his victory in 2016 by narrowly tipping those three states in Trump's favor.

A Quinnipiac University poll released this week found Biden leading Trump 53 to 42 percent in a potential head-to-head matchup in the state.

Then, Biden is expected to begin rolling out policy proposals over the next several months. He has already said at campaign events he plans to detail his approach to climate change before the end of May, and will also soon be releasing a plan to address student debt, as well as other proposals.

He is also devoting more time than most Democratic candidates to fundraising -- holding at least one fundraising event nearly every day he's been on the campaign trail, and allowing reporters to attend. One source familiar with the Biden campaign's approach said it has been much more aggressive in asking major Democratic donors to host events and raise specific amounts of money than other candidates -- many of whom entered the race focusing almost entirely on small-dollar fundraising and expecting to face the wrath of progressives for spending too much time with wealthy donors.

Because of Biden's later entry into the race, the end-of-June conclusion of 2019's second quarter will be the public's first detailed glimpse at his fundraising so far.

Biden also said this week he expects to begin preparing for the Democratic debates, the first of which take place June 26 and 27.

"I won't say I'm looking forward to it because I don't know how it's going to work" with so many candidates on stage, Biden told reporters this week. "But I'm anxious to be able to stand before people and say what I think and why I'm doing what I'm doing."