The shift to the left in Colorado on social issues that prompted Gardner’s altered stance was demonstrated by the decisive rejection of an anti-abortion “personhood” state constitutional amendment, by nearly two to one, 64.87 percent to 35.13 percent. Similar language had been rejected by Colorado voters by equally large margins in 2010 and 2008.

Gardner’s success indicates that in many swing states, the Tea Party and the Christian right will tolerate tactical apostasy and remain loyal on Election Day. In fact, the 2014 Republican primaries showed how weak the Tea Party had become, even in the South. Establishment Republican Senate candidates beat insurgents from the right across the board in Texas, Kentucky, South Carolina, North Carolina, Georgia, Kansas, Tennessee, Alaska and Mississippi.

The implosion of the Tea Party allows the Republican Party to shelve for the moment harsh deficit reduction policies that conservative analysts like James Pethokoukis at the American Enterprise Institute viewed as “the dodgy austerity economics of the Tea Party G.O.P.”

Despite the lessening of pressure from the populist right, indications are that the Republican leadership will be cautious in its efforts to address the party’s liabilities with the kinds of voters among whom Gardner made incremental gains in Colorado.

On Jan. 3, the Washington Post described Majority Leader Mitch McConnell’s plans for the 114th Congress. “On the things where we agree, the goal will be to make a law, not just put something on [Obama’s] desk.” Looking towards Republican chances in the 2016 election, McConnell noted that “the best thing we can do is to not mess up the playing field, if you will, for whoever the nominee ultimately is,” warning that

I don’t want the American people to think that if they add a Republican president to a Republican Congress, that’s going to be a scary outcome. I want the American people to be comfortable with the fact that the Republican House and Senate is a responsible, right-of-center, governing majority.

Unlike Gardner, McConnell is not setting out to confront and subordinate the right wing of his party, but rather signaling that he intends to keep it in check. The current Congress will test the viability of McConnell’s attempt to simultaneously achieve three goals. First, to prevent divisive forces from fracturing Republican unity, maintaining the party in a solid position going into the 2016 elections. Second, to restore the Senate itself as a national forum for debate. Third, to enact legislation of key importance to his business base, while – like Gardner – tacking toward the center on issues with particular value for public relations.

McConnell will have to balance these objectives as he shepherds controversial legislation: the Keystone XL pipeline, regulation of carbon emissions, tax reform, efforts to gut or weaken Obamacare, proposals to defund immigration initiatives, and so forth.

McConnell’s strength lies in his deep understanding of the Senate’s institutional practices and his talent for piecing together legislative proposals that resolve seemingly irreconcilable conflicts. In a January 2014 interview with the National Journal, he described his projected course as majority leader:

The committee process must be restored. The people we represent must be allowed to have a say through an open amendment process. And finally, we have to learn how to put in a decent week’s work on the floor again, because another thing we’ve lost around here is an appreciation for the power of the clock to force consensus.

He continued:

It won’t happen overnight. We’re all out of practice. But it’s a goal that I truly believe we can all agree on and agree to strive toward together. Because restoring this institution is the only way we’ll ever solve the challenges we face. That’s the lesson of history and experience. And we would all be wise to heed it.

McConnell and Boehner are both acutely aware that the lesson of recent history is that Republicans will overplay their hand, as they did after both the 1994 and 2010 midterm elections. Neither history nor demography, however, is political destiny. The Republican establishment, armed with the experience of their 2014 primary victories and the demonstrated success of Gardner’s tactics, will struggle to force the party back onto a mainstream course.

“I’ve asked my members to restrain themselves,” McConnell said in his interview with The Post. His ability to enforce restraint will be tested daily, if not hourly, over the next two years, most often by two Tea Party senators, Ted Cruz of Texas and Mike Lee of Utah. The outcome of the test of wills between McConnell and Cruz will shape the achievements of the 114th Congress, just as a similar struggle between Speaker John A. Boehner and Tea Party heroes like Louie Gohmert will in the House. Taken together, these battles will also provide intelligence about how the Republican Party will approach the 2016 elections.