Democrats are worried President Biden's stance toward Israel has ruined his standing with a key portion of the Democratic base, as the president continues to face criticism from progressives over his messaging on the war in Gaza.

"It has undermined one of his most important assets against Trump," Matt Duss, a former foreign policy adviser to Sen. Bernie Sanders, told Politico. "Biden’s reputation was — agree or disagree with him — he’s a decent guy, he’s an empathetic guy, he’s an honest guy. But this policy has been a cruel policy."

Sen. Tim Kaine, D-Va., Hillary Clinton's running mate in 2016, said there was an "obvious" answer to the problem that the president should have pushed for months ago. In a phone call on Thursday, Biden warned Israeli Prime Minister Benjamin Netanyahu that U.S. policy could change if he didn't improve the humanitarian situation in Gaza. 

"I applaud President Biden for successfully urging Prime Minister Netanyahu to open another border crossing from Israel to allow robust delivery of humanitarian aid," Kaine said in a statement last week. "But this was an obvious solution that should have happened months ago."

President Joe Biden

President Joe Biden speaks at a campaign event at Pullman Yards on March 9, 2024 in Atlanta, Georgia. (Megan Varner/Getty Images)

WORLD CENTRAL KITCHEN PAUSES GAZA OPERATIONS AFTER 7 AID WORKERS KILLED BY ‘UNFORGIVABLE’ ISRAELI AIRSTRIKE

Kaine said the current approach was "not working."

During a phone call with his Israeli counterpart, Biden stressed that Israel’s strikes on "humanitarian workers and the overall humanitarian situation are unacceptable," according to a White House readout of the call previously reported by Fox News Digital.

The same sentiment was echoed later Thursday by National Security Council spokesman John Kirby and Secretary of State Antony Blinken, with Blinken telling reporters that the United States would shift gears "if we don't see the changes that we need to see," according to the Jerusalem Post.

The 30-minute call came after seven aid workers with the World Central Kitchen were killed by Israeli airstrikes last week, adding to concerns about the humanitarian situation in Gaza.

Sen. Chris Van Hollen

Chris Van Hollen spoke to Margaret Brennan on Sunday about the White House's position on Israel. (Screenshot/CBS)

WHY MIDEAST NEIGHBORS WON'T OFFER REFUGE TO PALESTINIANS STUCK IN GAZA WAR ZONE

There reportedly was some concern in the White House ahead of the call with Netanyahu. A senior advisor said there was worry "Biden’s difficulty in controlling his Israeli counterpart could undermine his claim to steady competence in voters’ eyes," Politico reported.

Sen. Chris Van Hollen, D-Md., revealed on Sunday that he still isn't fully clear on the White House's position concerning aid and Israeli accountability amid the humanitarian situation in Gaza. 

"I was glad to see the president, at least as was reported out, finally say to President Netanyahu that if you don’t follow these — my requests — that there will be consequences, but the president and the White House have yet to lay out what consequences they have and what they want to impose. And we have had a situation where for months, the president has made requests to the Netanyahu government, they have ignored those requests, and we have sent more 2,000-pound bombs. We cannot revert back to that. We have to make sure that when the president requests something, that we have a means to enforce it," Van Hollen said. 

Joe Biden and Benjamin Netanyahu

Democrats have expressed concern that President Biden has ruined his standing among progressives with his support for Israel. (Getty Images)

CLICK HERE TO GET THE FOX NEWS APP

Sen. Bernie Sanders, I-Vt., has warned that while he believed what was going on in Gaza was "unspeakable," he argued that former President Trump would only make it worse if elected again.

 Fox News Digital's Michael Lee contributed to this report.