President-elect Joe Biden is expected to announce California Attorney General Xavier Becerra as his nominee for secretary of Health and Human Services in the coming days, according to three sources familiar with his plans. 

The selection of Becerra, who served 12 terms in Congress and was a member of House Democratic leadership before his appointment to replace Kamala Harris as California's top law enforcement official, comes as Biden's campaign has faced criticism from the Congressional Hispanic Caucus and Latino advocacy groups about the diversity of his future cabinet.

Becerra, who has taken on the Trump administration over immigration, health care, gun control and environmental rules in over 100 lawsuits, was thought to be a potential attorney general nominee for Biden, or even a successor to Harris in the Senate next year. 

The Congressional Hispanic Caucus encouraged Biden's senior aides to consider Becerra for that post, and New Mexico Gov. Michelle Lujan Grisham for the role of Health and Human Services secretary, in a call earlier this week, where members criticized Biden's transition over leaks regarding Lujan Grisham being offered another post in the incoming administration. 

Should he be confirmed by the Senate, Becerra would take a leading role in the Biden administration's coronavirus response efforts. 

Becerra, the son of Mexican immigrants, would be the first Latino to lead the department, and the second Latino nominated to serve in Biden's cabinet, after Alejandro Mayorkas, a Cuban immigrant and Biden's pick to lead the Department of Homeland Security.

A Biden transition spokesperson declined to comment on the planned announcement. Becerra's office did not immediately respond to messages seeking comment.

-ABC News' Benjamin Siegel, Katherine Faulders and Molly Nagle.

As many Republicans refuse to accept a Biden victory, Sen. Dick Durbin, D-Ill., said the focus should be on the coronavirus relief package.

“Joe Biden is going to be sworn in as the next president," he said on ABC's "This Week" Sunday. "I hope we don’t get embroiled in that debate further."

In a separate interview, however, Sen. Mike Braun, R-Ind., refused to acknowledge Biden's election win, despite the mounting legal losses and Republican-led states certifying results in the Democrat's favor.

"We've got a process and I think we have been going through it since the election, and it's going to play itself out," Braun told ABC News Chief Anchor GeorgeStephanopoulos.

Georgia Secretary of State Brad Raffensperger said he was disappointed that Trump didn't win in Georgia, but said there's been no evidence of systemic fraud.

"At the end of the day, we as Republicans didn't turn out enough voters. Our office, as secretary of state, is really just to look at what those votes totals were, and we report the results. And that's why it gets back to the state party (that) didn't do their job, didn't raise enough money and didn't turn out enough people," Raffensperger told ABC News Chief Anchor George Stephanopoulos on "This Week." Sunday.

In a meandering, nearly two-hour speech -- speckled with baseless claims of voter fraud, misleading statements about court cases and assertions he will be serving a second term -- President Donald Trump pushed for Georgians to get out on Jan. 5 for the runoff election that could determine control of the Senate.

With 48 Democrats (and liberal independents) and 50 Republicans, wins from Sens. Kelly Loeffler and David Perdue would lock up another two years of GOP control. If their opponents, Rev. Raphael Warnock and Jon Ossoff, respectively, win then Vice President-elect Kamala Harris would cast the deciding vote.

"Georgia patriots must show up and vote for these two incredible people," Trump said. "And I'm telling you, they're two of the finest people you'll ever meet. We can fight for the presidency and fight to elect our two great senators."

Trump spoke out against Republicans boycotting the runoff, saying the "radical left" would win if that happened.

The president tied the Democratic candidates to regular conservative targets like Sen. Elizabeth Warren, Rep. Alexandria Ocasio-Cortez and even Beto O'Rourke. He also repeatedly attacked Stacey Abrams, a former Georgia governor candidate, who helped organize Democratic voters and swing the state blue.

At one point, Trump even went on a tangent saying he did not want to attend the rally and didn't like helping other people. Oddly, he never explained what changed his mind.

"David and Kelly called and said, 'Will you do a rally?' I said, 'Not really,'" Trump regaled the crowd, referring to staffers coming to him to ask about doing the rally. "I said -- when they asked -- I don't do it for other people. It's a lot of work to do a rally."

Loeffler and Perdue were finally invited on stage to speak over an hour into the president's rally. Each spoke for only a minute or two before Trump took the microphone again.

Trump then went back to discussing the alleged transgressions against him in the presidential race. He went on to show a lengthy video of right-wing news media touting already debunked claims of fraud.

In the aftermath of Attorney General William Barr telling the Associated Press the Justice Department has not found evidence of voter fraud on a scale that could overturn the election, Trump was asked in the Oval Office Thursday whether he still had confidence in Barr -- but didn't directly answer.

"Ask me that in a number of weeks from now," Trump said.

Trump said the Justice Department "should be looking at all of this fraud" -- not just limited to civil issues -- and that Barr "hasn’t looked."

His comments come after Barr met with Trump at the White House following the Tuesday interview, with one source briefed on the meeting describing their interaction as "intense," but not elaborating with any additional details about the content of their discussion.

In the days after Biden was officially projected the winner of the election, Barr issued a memo to federal prosecutors authorizing them "to pursue substantial allegations of voting and vote tabulation irregularities" in the event there are "clear and apparently-credible allegations of irregularities that, if true, could potentially impact the outcome of a federal election in an individual State."

At the same time, Barr urged investigators to be vigilant against "specious, speculative, fanciful or far-fetched claims" that he said "should not be a basis for initiating federal inquiries."

But more than three weeks later, the DOJ and FBI have announced no such investigations relevant to the parameters of Barr's memo as an increasing number of states have moved forward with certifying their vote tabulations.

"Most claims of fraud are very particularized to a particular set of circumstances or actors or conduct," Barr said Tuesday. "They are not systemic allegations. And those have been run down; they are being run down."

The president on Thursday concluded that the election was “fixed” and “rigged” before refusing to answer follow-up questions. He made the comments during a jam-packed, largely maskless Oval Office ceremony in which he awarded the Medal of Freedom to football coach and Trump supporter Lou Holtz.

-ABC News' Ben Gittleson and Alexander Mallin