The throngs of Democratic candidates jumping into the 2018 congressional contests in hopes of 'resisting' President Trump have in turn fueled a nasty war within the party -- a fight that has seen incumbents scorned as primary fields swell.

This was witnessed most recently over the weekend, when the California Democratic Party declined to endorse Sen. Dianne Feinstein’s bid for a sixth term.

But in California and beyond, Democrats are experiencing internal tensions similar to what Republicans went through during the Tea Party wave of 2010. The open question: will they replicate the GOP's success of that cycle, or crumble amid their own divisions?

One potential risk is that moderate candidates will be pushed aside, in favor of liberal candidates who might not be as electable in a general election.

CALIFORNIA DEMOCRATIC PARTY WON'T ENDORSE FEINSTEIN

In Illinois, at least four Capitol Hill Democrats have endorsed the primary challenger over incumbent Rep. Dan Lipinski, a moderate seeking an eight term.

Illinois Rep. Luis Gutierrez, one of the four to back challenger Marie Newman, acknowledged the unusual, bare-knuckle move, while arguing it was necessary to show his party has “a response in the age of Donald Trump.”

“It’s not easy to endorse a challenger over a colleague in the House of Representatives, especially when that colleague is a member of your party,” Gutierrez told Capitol Hill reporters, when he and fellow Illinois Democratic Rep. Jan Schakowsky last month endorsed Newman, a businesswoman and first-time candidate.

Schakowsky also is a part of the leadership team for the Democratic Congressional Campaign Committee, which has yet to endorse Lipinski over the more liberal Newman, with the party primary less than a month away.

Newman also has an endorsement from potential 2020 presidential candidate and New York Democratic Sen. Kirsten Gillibrand and touts support from many of the progressive movement's biggest names -- including feminist icon Gloria Steinem, Emily’s List, Planned Parenthood, the Service Employees International Union and Indivisible, leaders in the resist-Trump movement.

“I don’t think we’ve ever seen this type of robust involvement by national Democrats picking winners and losers in their own primaries,” Caleb Burns, a partner in the Washington law firm Wiley Rein and who specializes in election law, said Monday.

The California Democratic Party's Feinstein snub reflected another such intra-party battle.

At the group’s annual convention, members gave Feinstein 37 percent of the vote, compared with 57 percent for state Senate leader Kevin de Leon. However, de Leon, a favorite of the state party’s progressive wing, didn’t get the endorsement either because he failed to garner the required 60 percent of the vote.

“With how far to the left the party has lurched, Democrats who do qualify for the general [election] are likely to be too extreme for their districts,” Republican National Committee spokesman Michael Ahrens said Sunday, echoing what moderate Democrats are purportedly telling DCCC leaders. “California Democrats made it clear that even Dianne Feinstein … is not nearly liberal enough for them anymore.”

Nowhere is the challenge of a candidate overload more glaring than in California, where the DCCC has targeted at least eight Republican-held House seats on their path to win a total of 24 and take control of the chamber.

However, the flood of Democratic candidates eager to capitalize on anti-Trump sentiment and the Republican-controlled Congress’ low approval ratings has created headaches for the DCCC, particularly in Orange County.

The group, whose mission is to get Democrats elected and re-elected to the House, has been hand-wringing for months over the situation. Group polling suggests so many Democrats are running in California’s top-two primary system that the splintered votes could hurt their ability to reach the general election, The Los Angeles Times reports.

Four races in Orange County were at the top of Democrats’ midterm list, considering 2016 presidential nominee Hillary Clinton won the conservative stronghold for the party for the first time in about 80 years -- in large part the result of the state’s Hispanic population migrating south from greater Los Angeles.

But in two 2018 races -- against incumbent GOP Rep. Dana Rohrabacher and retiring GOP Rep. Ed Royce -- eight Democrats have entered the fray.

A source tells Fox News that House Democrats focused on the midterms are at least suggesting to some candidates to withdraw.

The situation in Texas’s 7th Congressional District appears even more sharp-elbowed, with the DCCC openly opposing candidate Laura Moser, one of at least six Democrats running in a district Clinton also wrested from the GOP.

“Democratic voters need to hear that Laura Moser is not going to change Washington,” the group said last week. “She is a Washington insider, who begrudgingly moved to Houston to run for Congress.”

The DCCC also says in its website post that Moser as of last month was still claiming her Washington property as her primary residence to get a tax break and that she’s paid her husband’s D.C. political consulting firm more than $50,000 from campaign contributions.

“Whatever happens, I will continue to run a campaign on the issues, a campaign worthy of my daughter and all our daughters,” Moser, who this past weekend had actress Alyssa Milano on the campaign trail, responded on Twitter.

The DCCC has yet to respond to a request Monday for comment.

Beyond riding the anti-Trump sentiment, Washington Democrats are also relying on historical tailwinds to give them the House majority for the first time since 2010, considering the party that holds the White House typically loses about 30 seats in the first post-presidential race midterm.

However, recent generic ballot polls, in which likely voters say whether they’d prefer a Democrat or Republican for Congress, show Democrats’ big leads now down to single digits -- particularly after the GOP tax cuts.

“I think the tax bill is going to be a great benefit to Republican incumbents,” Burns also said. “They’re now able to explain a complicated law by pointing to the money that companies are putting back in people’s pockets. Voters can now see the results in structured, measurable ways.”

The conservative opposition research group America Rising said Monday: “As these contests unfold across the country, one thing is clear: Giddy talk of a coming ‘blue wave’ must be tempered with the ugly reality that the eventual Democratic nominees will not come out of these contests unscathed."