Senate President Pro Tempore Kevin de León (D-Los Angeles) displays a list of various backers of a climate change bill. (AP Photo/Rich Pedroncelli, File)

One of the most powerful Democrats in California — who is also one of the most senior Democrats in Washington — has her first serious challenge from the left.

State Senate leader Kevin de León announced Sunday he's challenging Sen. Dianne Feinstein for her seat in 2018. It's a bold move on de León's part, and in many ways it reflects where the Democratic Party is right now in the era of President Trump: divided on how much to stick it to Trump and whether its vision for the future should be unapologetically progressive.

Sen. Dianne Feinstein (D-Calif.) on Capitol Hill in May. (Cliff Owen/AP)

Feinstein and de León aren’t far apart on most policies. Where de León is hoping to distinguish himself most from Feinstein is his anti-Trump credentials. When he announced his run in an email to supporters, he literally accused the president of not having a soul.

"We now stand at the front lines of a historic struggle for the very soul of America, against a president without one."

Left unmentioned by de León were the echoes of Feinstein's words in August. She stunned an adoring San Francisco crowd when she said Trump could learn to be a "good president." The question is whether he can learn and change,” Feinstein said. “If so, I believe he can be a good president.”

Liberal groups in Washington have been looking for a moment like this to reshape a party they think has become too compromising on liberal values exactly when Democrats can least afford it. Consequently, they are thrilled about de León's decision to challenge Feinstein. He launched his campaign with the immediate endorsement of Democracy for America, a national group that formed from the remnants of Howard Dean's 2004 presidential campaign.

A super PAC formed by pro-de León California Democratic consultants launched an ad for him that starts off with Trump tossing paper towels in Puerto Rico. "This isn't normal," the ad says. "... It's clear that Washington's status quo has failed."

The left flank's defining narrative about de León is this: He's 110 percent anti-Trump and won't open the door to compromising with Republicans in a way that doesn't achieve a victory for the left.

"When Trump became President, de León didn’t ask people to sit back and wait, hoping maybe Trump would someday turn out okay," said Charles Chamberlain, executive director of Democracy for America, in a statement.

The California Senate race will probably be an extension of a fight the Democratic Party has been having with itself since Trump got elected. The moderate and liberal wings dug through the remnants of a terrible November and came to different conclusions.

The Bernie Sanders and Elizabeth Warren wing argued Democrats should have focused on a more populist message if it wanted to reach the white working-class voters that broke for Trump in higher-than-expected numbers.

"We won't defeat Trump and his Republican Party with corporate Democrats pushing Republican-lite policies and weak leadership," Chamberlain said.

Moderates are skeptical that turning the party to the left will solve Democrats' problems.

"It didn't matter what type of Democrat you were on Tuesday," Jim Kessler, of the centrist Democratic think tank Third Way, said in the days after the election. "You were defeated. . . . every element of the party has to look in the mirror and reassess, and say 'What can we do better?' "

That wing of the party argues that the power Feinstein has amassed in a quarter century in the Senate is what will make the difference against Trump.

She's the top Democrat on the Senate Judiciary Committee, which is investigating aspects of the Trump campaign's connections to Russia — including the meeting Donald Trump Jr. held at Trump Tower with Kremlin-connected Russians during the campaign. She's also one of the top Democrats on the Senate Intelligence Committee, which is taking the lead in Congress on investigating potential Trump-Russia collusion.

And she was one of the first in Congress to call for a ban on a deadly gun accessory used in Las Vegas, bump stocks, a ban the White House ultimately said it would consider.

As for whether de León can win, both sides have their arguments. Feinstein is one of the most popular politicians in California, and she can self-dfund millions.

De León's supporters argue his back story as the son of Guatemalan immigrants and recent legislative record of guiding his chamber to pass a single-payer health-care bill will be enticing for Democrats sick of the establishment (though he supported Hillary Clinton over Sanders, and there's some evidence he's not fully embraced by liberal leaders in the state).

De León might not have the primary to himself, either. Environmentalist and billionaire Tom Steyer said Sunday he's still considering challenging Feinstein.

California has a jungle primary system, where all candidates are on ballot, regardless of party, and the top two vote-getters advance to the general election. Both sides argue that system will benefit them.

Either way, in a state as blue as California, that means this intra-party Democratic battle could play out for the next 13 months.