For Kentucky Sen. Mitch McConnell, enough was enough.

The Senate's top Republican had watched a Tea Party-driven government shutdown sink the GOP's already-weak brand and jeopardize McConnell's own chances of ever becoming majority leader. The solution, he concluded, was that the party's so-called Establishment had to start fighting back against its most conservative wing.

McConnell, an ardent Obamacare opponent, and other Republican pragmatists in Congress, supported the conservatives' mission to defund Obamacare during budget negotiations, which led to the 16-day shutdown. But the pragmatists also accepted that their odds of success were virtually nil. Democrats ruled the Senate and White House, those lawmakers argued, and Obama was never going to allow his signature legislative achievement to be scrapped just because the political opposition demanded it.

Yet, Republicans who wanted to avoid a shutdown watched it happen anyway. Tea Party-aligned Republicans, backed by outside groups that threatened any GOP lawmakers who didn't go along, had prevailed despite the widespread concern that such a shutdown would be politically disastrous for the party.

Dismayed Establishment Republicans, frustrated again by an increasingly influential community of conservative insurgents, reasserted themselves in the wake of the shutdown and demonstrated a new resolve to fight back — something they were once reluctant to do.

“There were people who were basically afraid of 'em, frankly,” McConnell told the Washington Examiner. “It’s time for people to stand up to this sort of thing.”

McConnell worries that the Senate Conservatives Fund and other insurgent groups are pursuing a confrontational, uncompromising strategy that makes it impossible for conservatives to govern.

“The Senate Conservatives Fund is giving conservatism a bad name. They’re participating in ruining the [Republican] brand,” McConnell said. “What they do is mislead their donors into believing the reason that we can’t get as good an outcome as we’d like to get is not because of a Democratic Senate and a Democratic president, but because Republicans are insufficiently committed to the cause — which is utter nonsense.”

The outside groups, in McConnell's view, are unaccountable and financially motivated and pose a threat to the Republican Party's viability. The groups in 2010 and 2012 backed a handful of untested, ideological candidates in Republican primaries that couldn't win general elections, costing the party opportunities to build a majority. It's a threat that must be addressed ahead of the 2014 and 2016 elections, McConnell said, because it's repelling the very voters the GOP needs if it's ever to take control of the federal government.

“To have the kind of year we ought to have in 2014, we have to have electable candidates on November ballots in every state — people that don't scare the general electorate and can actually win, because winners make policy and losers go home,” McConnell said. “We can't just turn the other cheek and hope for the best. It didn't work in 2010 and 2012 so we're going to try something different in 2014.”

McConnell faces his own threat from the Senate Conservatives Fund, which is backing a Republican primary challenger against him in 2014. McConnell already faced a serious challenge from a Democrat, Kentucky Secretary of State Alison Lundergan Grimes, in his bid for a sixth term. SCF's involvement now means he'll have to spend time and money he otherwise would not have spent just to win the GOP nomination.

Immediately after the government reopened in mid-October, McConnell launched a very public offensive against SCF, the main instigator of the defund-or-shutdown strategy which actually ran ads attacking Republicans who opposed the tactic.

McConnell went so far as to ban any political vendors from getting any additional business from Republicans' Senate campaign arm if the vendors did any work for SFC, a group founded by a former Republican senator, Jim DeMint.

But McConnell is on a broader mission with implications that reach far beyond his dispute with SCF. The Republican leader intends to reassert the power of the GOP's pragmatic wing — the so-called Establishment — in the party's nominating process and legislative agenda ahead of the 2014 congressional elections and the 2016 presidential race.

McConnell's decision to single out SCF for rebuke was not impulsive. The minority leader spent months trying to determine how to combat advocacy groups with growing political muscle. The groups, he said, threaten to jeopardize the GOP's relationship with voters through well-financed negative advertising. They also discourage the kind of pragmatic conservative governance that recognizes the reality that Democrats control the Senate and White House.

This past summer, McConnell drafted a letter to SCF practically daring the group to endorse Louisville businessman Matt Bevin, a fellow Republican who is challenging McConnell in next year's primary. McConnell decided against sending the letter but wanted to relay the message that Republicans would not be intimidated. SCF endorsed Bevin in October, after McConnell negotiated an end to the government shutdown, citing the Senate leader's role in reopening the government as evidence that he wasn't committed to conservative principles.

Soon after he helped reopen the government and avoid a default on the national debt, McConnell headed home to Kentucky, where he spent a week talking with prominent GOP insiders about his plans to fight back against the conservative insurgency. McConnell's allies said he received broad encouragement to engage.

Matt Hoskins, SCF’s executive director and sole decision maker, said McConnell will pay a political price for opposing an organization that gets much of its support from grassroots members of the party. Hoskins dismissed McConnell's claim that SCF and groups like it are a threat to Republican election victories. He charged that McConnell is worried only about his own re-election.

Hoskins is unapologetic about SCF's aggressive tactics against other Republicans. The group embraces quality conservative candidates, he said, including four Senate contenders in 2014.

“Grassroots conservatives are very worried about the direction of the country and they believe urgent action is needed to save it,” Hoskins said. “This is why they're not happy with politicians who vote with them most of the time. They want people who will actually stand up and fight for them.”

McConnell isn't alone in his battle against the conservative insurgents. Groups like the U.S. Chamber of Commerce, unnerved by the government shutdown and near-default, plans to be more active in 2014 backing business-friendly candidates against conservatives in GOP primaries.

The group in October spent heavily to help Bradley Byrne, a former state senator, beat a more conservative contender in a special GOP primary election in Alabama.

Republican pragmatists have talked for years about fighting back against the conservatives who pulled the entire party further to the political Right. Nothing ever came of that talk, many of those Republicans say, until now. The politically disastrous government shutdown and the uncompromising posture of conservatives has pushed the GOP Establishment to a tipping point.

“I’ve heard this story for years and nothing’s happened,” a Washington-based Republican strategist said of the pragmatists' stand. “But I’ve seen more happen in the last two months than I’ve seen in the last four years.”