Has the Trump wing of the GOP handed Democrats an opening to retake the Senate?

Sen. Jeff Flake’s surprise decision against seeking reelection marked a major victory for Stephen K. Bannon and his pirate band of Republicans. But the larger question Wednesday was whether the insurgency will cost the GOP its thin majority on Capitol Hill.

The fratricide that Bannon, a former White House advisor, is waging against President Trump’s critics threatens to undermine the party’s Senate hopefuls and has already lifted Democratic prospects, boosting the possibility of shaving the GOP’s 52-48 majority or eliminating it altogether.

“It’s causing Republicans to spend money defending their own rather than focusing on the big target, which should be expanding the size of their governing majority,” said Scott Reed, chief political strategist for the U.S. Chamber of Commerce, one of the citadels targeted by Bannon and his anti-establishment forces.

The insurgency also runs the risk of putting forth candidates unable to broaden their support beyond a fervent but small wing of the GOP, repeating the failings of the tea party movement that cost Republicans winnable Senate seats in 2010 and 2012.

“It’s too soon to say that the majority is in play,” Jennifer Duffy, an expert on Senate campaigns, wrote in a recent analysis for the nonpartisan Cook Political Report. But, she went on, “If the national political environment further deteriorates for Republicans … or they nominate a train wreck or two, Democrats could have a shot at winning the narrowest of majorities.”

Naturally, those leading the revolt see matters differently.

“The candidates who are going to win in 2018 are going to be the candidates who position themselves against Washington, D.C., against [Senate Majority Leader] Mitch McConnell and against the Republican establishment,” said Andy Surabian, Bannon’s White House deputy and a senior advisor to the Great America Alliance, a political action committee that backs Trump and outsider candidates.

Not long ago, Republicans spoke plausibly of padding their Senate majority, even approaching a 60-vote, filibuster-proof majority.

But that was before Trump took to belittling Arizona Sen. Flake and Tennessee Sen. Bob Corker — both of whom have announced plans to step down after 2018 — and before Bannon, upon exiting the White House, announced a “season of war” against Republicans who prove less than stalwart in their support of Trump.

Bannon and his allies have begun seeking tens of millions of dollars to finance a slate of “economic nationalist” candidates to challenge GOP incumbents and, if successful, overthrow McConnell. Trump has not discouraged the effort.

Flake, who criticized the president during the 2016 campaign and, unlike many Republicans, kept up the critique after Trump took office, was a prime target of Bannon and his forces.

But his exit could ultimately jeopardize the GOP’s Senate majority if it serves to elevate Kelli Ward, a former state senator and Bannon-favored candidate who has demonstrated little appeal beyond Arizona’s hardest-core conservatives. She has emerged, at least temporarily, as the front-runner for the nomination.

For that reason, establishment Republicans were scrambling, searching for a candidate with broader support who could increase the chances of Republicans hanging onto the seat.

The departure of Corker is more clear-cut: It put a safe GOP seat in danger by possibly ushering Democrat Phil Bredesen into the race; the former two-term governor may be the only Democrat with a shot at winning in a state Trump carried by nearly 30 points.

That dynamic, broadening the map of competitive states, is what gives Democrats hope as they look to 2018.

The mathematics remain daunting and odds continue to favor continued GOP control. Thirty-four seats will be on the ballot and Democrats must defend 25, compared with just nine for the GOP.

To take control of the Senate, Democrats need to keep every seat they now hold — no small feat — and pick up three held by Republicans. In addition to trying to flip a seat in Arizona, Nevada is a prime target. There, GOP Sen. Dean Heller — vulnerable in a state Hillary Clinton carried — is facing a Bannon-backed primary challenger.

Similar intraparty fights could boost Democratic incumbents facing reelection in West Virginia, Montana, Indiana, Ohio and Pennsylvania — all states that Trump carried in 2016.

Another danger for Republicans might be called the “Akin effect.”

In 2012, GOP Rep. Todd Akin torpedoed his Senate candidacy in Missouri by raising the matter of “legitimate rape” in a discussion of abortion policy. Worse, from a Republican perspective, was that candidates across the country were forced to respond to his unaccountable explanation that “the female body has ways to try to shut the whole thing down” and avoid pregnancy.

Similarly, the likely election of Roy Moore, the Bannon-backed candidate in Alabama’s special Senate election, will introduce to the national conversation his provocative views on matters such as outlawing homosexuality and banning Muslims from Congress. Republicans everywhere will doubtless be asked to weigh in, or be seen ducking the questions.

“This is not a man who will disappear until the next election,” Alabama political columnist Kyle Whitemire wrote this week. “He will use that new platform to preach his message every opportunity he gets. And cable TV news shows will be more than eager to give it to him.”

Of course, any political prognostications this far removed must be viewed with some skepticism. The field in various Senate contests has yet to be determined and the political climate can change, and change again, at the speed of a tweet.

“We’re basically a year out from the election,” said Sam Nunberg, a former Trump campaign aide closely allied with Bannon. “How do these so-called geniuses … know what will happen? I seem to recall many of these people said Donald Trump would never win.”

mark.barabak@latimes.com | Twitter: @markzbarabak

michael.finnegan@latimes.com | Twitter: @finneganLAT

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