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Mitch McConnell and his allies ready for war with Steve Bannon

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Senate Majority Leader Mitch McConnell, R-Ky., leaves a meeting with President Donald Trump on his tax reform agenda, Capitol Hill in Washington, Tuesday, Oct. 24, 2017.

Senate Majority Leader Mitch McConnell, never afraid of hardball politics, is determined to finish the Republican civil war that Steve Bannon started.

“This guy has extraordinarily toxic relationships and views,” Josh Holmes, McConnell’s former chief of staff and a close confidant, said of Bannon in an interview with the Washington Examiner. “If we’re not talking about him in October of 2017, the Democrats will be talking about him in October of 2018.”

President Trump’s former chief White House strategist is recruiting candidates to challenge Republican incumbents in 2018 primaries, with the main goal of ousting McConnell’s allies and replacing him as majority leader.

Related: Steve Bannon's revolt against Mitch McConnell gets underway

After deliberating how seriously to treat Bannon’s threats, and taking a cue from the Kentucky Republican, “McConnell World” — the majority leader, his super PAC, and cadre of Senate office alumni and other allies sprinkled throughout Republican politics — decided to join the fight and escalate it.

Senate Leadership Fund, run by McConnell alumnus Steven Law, posted a tweet within days that accused Bannon of being anti-Semitic based on a news story from the 2016 campaign, and asked Danny Tarkanian, the challenger he is backing in the primary against Sen. Dean Heller, R-Nev., if he supported the views of his benefactor.

“We’re litigating the issue of Steve Bannon and all of his baggage now so that hopefully by the end of the year, we’re fully focused on Democrats,” SLF spokesman Chris Pack said. “It is important for Republican candidates to understand the drag that Steve Bannon will be in the general election if they get too close to him.”

Last week’s attack from McConnell’s super PAC, was only the first salvo in what his associates say is a long-term commitment to defang and delegitimize the Breitbart News chairman.

Bannon left Breitbart News in August of 2016 to serve as the CEO of Trump’s presidential campaign. He then moved into the West Wing as chief strategist. Bannon left the White House in August and returned to Breitbart, a conservative news website that has been strongly supportive of Trump and linked to the "alt-right."

Using the megaphone and establishment legitimacy afforded him through his affiliation with Trump, Bannon is meeting with Republican donors, speaking at think tanks, and headlining official GOP grassroots events, to garner support for removing McConnell as majority leader.

“McConnell World” watched this unfold for about a month without doing much about it.

That changed in late October. With Trump by his side during a news conference at the White House, McConnell specifically criticized Bannon and some of the candidates he is backing in 2018 GOP primaries as a politically dangerous for the party and the president.

The Kentuckian, in his sixth term, is deliberate about responding to attacks, which routinely come his way because of his leadership post. So McConnell World saw his broadside against Bannon as a signal to engage.

As McConnell moves to drive a wedge between Trump and his former chief strategist, more attacks from his allies are in the pipeline. After watching what they view as uncritical press coverage of Bannon emanate from his attacks on McConnell, they have made a strategic decision to take Bannon seriously and go on the offensive.

Bannon and his insurgent supporters don’t think McConnell’s approach will work.

The majority leader’s approval numbers are underwater with a Republican base that is angry with their party’s establishment. These voters, the insurgents contend, aren’t likely to be swayed from supporting challenger candidates because of arguments that Bannon is a racist (which they deny.)

“McConnell, Holmes and Law are coming to a battle that they don’t know how to fight. Every time they attack Steve they’re playing directly into his hands, and he knows it,” a political operative close to Bannon said. “Their phony tough guy act only reveals how desperate they truly are.”

Bannon’s stock rose after a special Senate election in Alabama in September. McConnell’s candidate in that race, appointed Sen. Luther Strange, lost a runoff contest to Bannon’s pick, retired Judge Roy Moore. Polling showed that McConnell’s support for Strange was a factor in the outcome — and not to the incumbent's benefit.

The failure to move through the Senate legislation repealing and replacing Obamacare created some doubts about McConnell’s leadership. But the majority leader, through a mixture of patience and grit, has weathered past storms, maintaining his position and eventually vanquishing adversaries.

“He’s experienced, and unemotional, and tough,” said Sen. Lamar Alexander, R-Tenn., friends with the majority leader since both were Senate aides more than four decades ago. “He’s been majority leader, or Republican leader, longer than almost anyone.”

McConnell has no qualms about playing rough, and he subscribes to the philosophy that its better to tear apart his political foes, even at the risk elevating their name identification and stature, than to let attacks go unanswered.

The majority leader prosecuted that strategy successfully in 2014 in his Senate primary against an anti-establishment challenger, Matt Bevin, who is currently the governor of Kentucky.

McConnell used that approach to defeat insurgent challengers in a handful of other Senate primaries that year that he believed would have been liabilities in the general election. Nominating such candidates in 2010 and 2012 cost the GOP a chance at winning the Senate majority.

He is doing it again this cycle. Shying away from a fight, Holmes said, “is not how McConnell World operates. They are willing to get their hands dirty.”