Since his arrival in the 2020 presidential race, Joe Biden has basked in his status as an early frontrunner: he has coasted in most early battleground and national polls, touted formidable fundraising numbers and remained squarely focused on a potential general election matchup with Donald Trump.

But this week, the former vice-president stumbled as he skipped not one, but two progressive gatherings and flip-flopped on a key abortion rights policy after being criticized by his fellow Democratic contenders.

The events ignited fresh questions over whether Biden’s campaign is geared to withstand a crowded Democratic primary, where candidates must first court an increasingly progressive base before eyeing Trump’s grasp on the White House.

Related: Watch Elizabeth Warren blast Biden for his stance on abortion funding

Biden, who has centered much of his candidacy around the notion of electability, will be missing in action on Saturday as nearly all other Democratic presidential candidates appear at the Iowa Democratic party’s annual hall of fame dinner.

His decision to forgo the cattle call in the first state to hold its caucus in 2020, comes on the heels of his absence at last week’s California Democratic party convention and a forum hosted by the progressive group MoveOn.org.

“I think, quite frankly, they’re afraid of the showing he would have in these settings,” said Brian Fallon, a former aide to Hillary Clinton’s 2016 presidential campaign. “These are settings where his frontrunner status might come under question if he got a low-key reception.”

He added: “You can potentially draw the conclusion that he’s not courting these audiences, but I think they’re afraid of a press narrative that might emerge if two, three, four other campaigns have a lot more enthusiasm.”

The Biden campaign did not return a request for comment.

Since formally launching his campaign in April, Biden has kept a light campaign schedule and held far fewer events than the other Democrats jockeying for the top of the party’s 2020 ticket. As the most experienced and well known entity in the field, he has instead focused on raising money and staying above the fray.

His record on domestic and foreign policy issues – ranging from abortion and criminal justice to immigration – has nonetheless remained a subject of scrutiny. Biden’s reluctance to directly engage with progressive voters has been received by some as a dismissal of their concerns.

The ongoing questions surrounding Biden’s past record were laid bare this week when he visibly struggled to explain his position on a controversial US policy barring the use of federal funds for abortion services. The 40-year-old ban, known as the Hyde amendment, makes exceptions for victims of rape and incest or to save a mother’s life.

While campaigning in South Carolina, Biden was caught off guard when approached by an activist with the American Civil Liberties Union who implored him to endorse an end to the Hyde amendment. Biden appeared to come out in favor of overturning the provision, only for his campaign to clarify that he still supported the ban.

The backlash from other 2020 contenders, as well as progressive and pro-choice groups, was swift and severe.

“This is not about politics, what this is about is about healthcare, about reproductive freedom, about economic freedom and about equal opportunity for all women,” Massachusetts senator Elizabeth Warren said at an MSNBC town hall on Wednesday. “Now, some got lucky from what happened and some got really unlucky on what happened.”

The Hyde amendment, she added, has “been wrong for a long time.

“Because it really is, it’s just discrimination.”

Vermont senator Bernie Sanders also rebuked Biden’s stance in a tweet that did not mention his rival by name, but stated: “There is #NoMiddleGround on women’s rights. Abortion is a constitutional right. Under my Medicare for All plan, we will repeal the Hyde Amendment.”

The reaction offered a glimpse of the pushback Biden is likely to face as the first Democratic primary debates are held later this month, and the skepticism he might face from progressive crowds and activists.

Karen Finney, a Democratic strategist, pointed out that doing away with the Hyde amendment was both a part of the Democratic party platform in 2016 and a focal point of Hillary Clinton’s agenda.

“Biden failed to recognize that the core of the Democratic party is in a very different place,” she said. “Repealing the Hyde amendment is in the party platform, and we are not going backwards.”

“The issue is even more acute in the wake of increasingly draconian GOP laws that disproportionately target women of color.”

By Thursday, Biden reversed his view and came out in favor of repealing the Hyde amendment, stating: “If I believe healthcare is a right, as I do, I can no longer support an amendment that makes that right dependent on someone’s zip code.”

“I can’t justify leaving millions of women without access to the care they need and the ability to ... exercise their constitutionally protected right,” he added.

Biden framed his evolution in part around a spate of extreme anti-abortion laws, pushed by Republican lawmakers across the country, that he said threatened women’s access to abortion. At the same time, he said he was making “no apologies” for his prior support for the Hyde amendment.

Related: Who is trying to ban abortion in the US? – podcast

Fallon said the row over abortion was a microcosm of the kind of challenges Biden might encounter at the progressive gatherings he has thus far avoided.

“There’s been a recognition that the backbone of the party are people of color and women,” he said, while adding the Biden campaign had “misjudged” the temperature within the party on abortion rights. “It is not an issue that you can ‘find a middle ground on’.

“I suspect that there’s going to be more issues that are going to come up where his approach of positioning himself as the centrist – and appealing to the moderates of the party – is going to run headlong into some positions where they might think they can stiff arm the left, but in the context of a debate stage are not going to play well.”