There are two power centers in the Senate Republican Conference. One is the official leadership under Minority Leader Mitch McConnell. The second is the Tea Party Troika of Ted Cruz, Mike Lee and Rand Paul.

It's not that there are two Republican parties. Nor is there a chasm running along ideological lines. The new dynamic is this: The official leadership has even less power than Senate leadership typically has, and the Tea Party Troika, mastering what's called the "inside-outside game," has more power to swing their colleagues than backbenchers normally have.

Senate floor leaders are typically called "cat herders." Individual senators always have much more power than individual congressmen, so party leaders in the upper chamber always have trouble corralling their flock. McConnell has even less leverage than his predecessors.

First, the GOP earmark ban in effect since the 2010 elections makes it harder for party leaders to buy off wavering members.

Second, the persistent anti-establishment sentiment among the GOP base blunts leadership threats involving committee assignments. Among the GOP base, it's a badge of honor to be whacked publicly by the leadership. Rep. Justin Amash, R-Mich., became something of a Tea Party hero when the House leadership stripped him of committee spots because he wouldn't do the party's bidding.

Third, McConnell has lost many allies, often in contests with the Tea Party. Lee and Paul both came to the Senate by beating McConnell intimates. Lee ousted McConnell confidant Bob Bennett in a 2010 Utah GOP nominating fight, and Paul bested McConnell's handpicked candidate for the open Kentucky Senate seat that same year.

Retirements have claimed McConnell's other closest advisers -- Judd Gregg, Jon Kyl and Kay Bailey Hutchison have all joined the private sector.

Meanwhile, Cruz, Lee and Paul have more clout than three first-term senators normally would enjoy.

Solidarity is one factor. Having to defeat K Street and the GOP establishment to win their jobs has created a bond among the three.

Most of the Troika's clout comes from its ability to rally the party's grass roots, which then lean on other senators to take the conservative hard line. That's what happened in the gun control debate.

Cruz, Lee and Paul put out a public letter in March promising to filibuster the motion bringing the gun control bill to the floor. Cruz, in a meeting with activists, explained that the letter was carefully timed to appear just before the congressional recess.

"Once that letter was out there, senators would go to their home states. They'd show up at a town hall, and men and women from their state would stand up and say: 'Hey, why aren't you standing up for the Second Amendment? What's wrong with you? If these guys are fighting, what are you doing?' "

With gun control, that pressure helped move a dozen Republicans to sign the filibuster letter. Eventually most Senate Republicans voted with Cruz, Lee and Paul to filibuster the motion to proceed.

It's the Tea Party whip operation. It's called the "inside-outside game," because a few folks on the inside -- senators and groups like FreedomWorks, Club for Growth, Heritage Action and the National Rifle Association -- are able to rile up a bunch of folks on the outside. Those outside players are noisy constituents, local party operatives, talk radio hosts, and donors, so they have more sway over individual senators than the party leadership.

Sometimes the mechanism for reaching the grass roots is simply the megaphone of being a U.S. senator. Paul's 13-hour filibuster against drone strikes on U.S. citizens was a prime example.

But outside groups are a key tool. The NRA rallied its membership to hold the line that Cruz and crew drew during the gun debate. When the Club for Growth or Heritage Action announce they are scoring a particular vote, members know that voting wrong will trigger donor and grassroots anger.

And these outside groups can reach into every state and congressional district. FreedomWorks has become something of a hub for Tea Party organizations. Heritage Action holds a weekly conference call with a top tier of activists it calls "sentinels." Heritage Action arms the sentinels with inside-the-Beltway intelligence, and the sentinels keep an eye on when lawmakers have town hall events.

The result: Many GOP senators are just as worried about Ted Cruz's approval as Mitch McConnell's.

Timothy P. Carney, The Washington Examiner's senior political columnist, can be contacted at His column appears Monday and Thursday, and his stories and blog posts appear on