PHILADELPHIA — Bill Clinton was once the Democrats explainer-in-chief, electrifying the convention crowd with his support of President Barack Obama.

Today, he increasingly seems to be explaining himself.

In the four years since the party’s last national convention, the center of gravity in Democratic politics has shifted decidedly to the left. Clinton must finesse some of his administration’s biggest achievements, including a landmark free trade agreement and major criminal justice law, lest his wife pay the price with the party’s emboldened liberal base.

Tonight, the former president will promote what aides say are his wife’s lesser-known achievements, her early days as a child advocacy lawyer, her policy campaigns as first lady and work as senator from New York.

But his 10th consecutive convention address may require one of the toughest balancing acts of his career: separating his wife’s legacy from his own.

“It’s not just (Bernie) Sanders supporters who have concerns about the impacts of those policies,” said Ben Jealous, a former head of the NAACP who endorsed the Vermont senator and now backs Clinton. “You look at this platform and in many ways it’s a response to those policies.”

There’s little question Bill Clinton remains a beloved figure within the party; he’s hosting a series of his own events during the convention, where top donors to his wife’s campaign will fete him after his speech.

At the same time, some of the key achievements of his administration formed the basis of rival Sanders’ critique against his wife, particularly among younger voters — that she’s too willing to compromise liberal ideals for political gain.

“His presidency was a little bit before my time,” said Mike Cordaro, 29, of Blueskin Township. “From what I know now, looking back, I’m really not a big fan.”

Separating Bill Clinton’s achievements from Hillary Clinton’s record proved difficult for her campaign during the primary season, particularly after years of the couple famously marketing themselves as “two for the price of one.”

Clinton has made clear that her husband will be playing a key role in her administration’s economic policy, doing far more, she has said, than picking “the flowers and the china.”

“It’s an all-hands-on-deck time,” she said in a weekend interview with CBS’s “60 Minutes.” ‘’And there’s a lot that happened which helped the American people during those eight years.”

But that period is now getting a skeptical re-examination within a party that’s grown more liberal under the Obama administration.

Much of what Sanders supporters held against Clinton — her support for free trade, late backing of gay marriage and criminal justice reform — were positions of the Clinton administration. Sanders made reinstating Glass-Stegall, a Depression-era banking law repealed under Bill Clinton’s administration, a central attack line of his campaign.

Those issues were seized upon by protesters who followed the Clintons across the country loudly denouncing the North American Free Trade Agreement and the 1994 crime bill — two key pieces of Bill Clinton’s legacy. Clinton himself has said that he regrets approving the Defense of Marriage Act and the “don’t ask, don’t tell” policy that banned gays and lesbians from military service.

He also has looked back with regret on signing the crime bill, which led to tougher sentencing for drug offenses.

Still, the attacks, which Clinton believed were stoked by Sanders, infuriated the former president, who was still calling top campaign staff to complain about Sanders’ tactics long after it was clear the Vermont senator could not capture the nomination.

And at times, despite efforts by campaign staff to limit him to smaller events and fundraising, Bill Clinton’s free agent ways exploded into public. He sparred with Black Lives Matters protesters who interrupted his campaign speech in Philadelphia in April and sparked outrage for dropping in for a private chat with Attorney General Loretta Lynch while her Justice Department was investigating his wife’s email server.

Clinton backers stress that the former president remains more of an asset than a liability. They argue he’s one of the most popular former presidents, is among the party’s best fundraisers and is most effective messengers on her behalf.

“He’s got to remind America of what a presidency under Donald Trump would look like,” said Maryland Rep. Elijah Cummings. “Nobody can do it better.”