Until Thursday, Joe Biden stood his ground against Democratic critics.

In recent weeks, the front-runner for the Democratic presidential nomination defended the 1994 anti-crime law he wrote, refused to give Anita Hill a satisfactory apology, joked about touching too much, deflected on his past support for gun rights, and remained silent about his crusade to stop busing as a means of desegregating schools.

It was as if Biden wanted to prove, by refusing to yield to the base of his own party, that he had the mettle and moderateness to take on President Donald Trump. The mettle would matter to Democrats in the primary and the moderateness to swing voters in a general election.

All of it played into the trait Biden fans so often cite first when talking about him: authenticity.

But then, in a fit of awkward acrobatics that could damage his image, Biden quickly whirled through positions on abortion — a matter of deep religious, moral and practical consequence to millions of Americans — and landed, with a big wobble, on the left.

For decades, Biden was a vocal proponent of the Hyde Amendment, which bans federal funding for abortion, except in cases in which the life of the expectant mother is in danger or she is the victim of rape or incest. Most members of Congress, including all of the current and former lawmakers running for president in 2020, have voted for larger spending bills containing the Hyde language, but Biden's major rivals have said they oppose the provision itself.

Last month, to little fanfare, Biden told an ACLU activist that he would roll back the Hyde amendment.

But his campaign told NBC's Heidi Przybyla, in an article published Wednesday, that he still supported the provision, touching off explicit and implicit criticism from abortion-rights groups, Democratic activists and even some of his rivals for the nomination. He was getting pounded.

Ironically, for a candidate long thought to be most prone to inflicting self-harm through an off-the-cuff remark, this was no gaffe. But it did turn into a major mistake — and one that could cost him in the long run.

By Thursday, Biden found himself on stage at a Democratic National Committee gala in Atlanta carefully explaining that he had changed his mind. Though he'd been lashed by fellow Democrats, he still wanted to present himself as unbowed by pressure.

"I make no apologies for my last position, and I make no apologies for what I’m about to say," he said. "I can’t justify leaving millions of women without access to the care they need and the ability to ... exercise their constitutionally protected right. 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."

And still, Biden said, if the threat of accessibility for poor women was removed, he might revert to favoring the Hyde amendment.

Kate Bedingfield, deputy campaign manager for Biden, declined to reveal whether he was counseled on the decision in the day that it took him to reverse a position he'd held for decades.

"Not going to get into any private discussions," she wrote in a text message.

The fear that he might have damaged his narrative was evident enough that Rep. Cedric Richmond, D-La., a co-chair of the Biden campaign, used the word "authentic" three times to describe him in a brief interview Thursday night.

"The one thing that Joe Biden is that everybody has to know is that he's authentic," Richmond said. "And that was authentic Joe Biden speaking from his heart ... So, look, he is who he is. And that is an honest, candid, authentic man."

For the moment, Biden has pacified some critics and probably prevented donors and voters from jumping ship.

But his reaction may have chipped away at his narrative — and at confidence in his decision-making — in ways that hurt him over the course of time. Being on both sides of an issue is seldom a good look politically. Swing voters will see Biden buckling to his base, and Democrats are unlikely to reward him for coming late to a position that is pretty universally accepted in their primary field.

One consequence may be a new willingness among fellow 2020 candidates to take him to task directly for his past. In addition to the quick pile-on of hopefuls spreading word of their opposition to Hyde while he was struggling with it, Rep. Seth Moulton, D-Mass., a veteran who has yet to gain traction in the polls, applauded Biden on Twitter for his reversal and then sniped “Now do the Iraq War.” Biden famously supported authorizing President George W. Bush to invade that country more than 16 years ago.

"The @JoeBiden rollout was close to flawless," David Axelrod, the former aide to President Barack Obama, wrote on Twitter. "His handling of this Hyde Amendment issue was a mess. Changes of position over a long career are justifiable but should be thoughtfully planned. This was an awkward flip-flop-flip."