“The base is not about personalities, it’s about trusting that you will fight for the things I believe in,” says another conservative aide. “Rubio never really did anything before immigration reform to build up that trust, and he hasn’t done anything since then to stand out and say to conservatives: ‘You were right about me, I will stand, fight, and take shots from the establishment.’”

Enter Ted Cruz. Like Rubio, he ran against and defeated the establishment GOP candidate. Cruz promised to shake things up, to be a different kind of senator. “If I go to Washington and just have a good voting record, I will consider myself a failure,” he said repeatedly on the campaign trail. He has certainly lived up to his promise, most recently by leading the effort to defund Obamacare, battling considerable skepticism from members of his own party and waging a 21-hour filibuster on the Senate floor in defense of the strategy. Meanwhile, Cruz’s voting record, as scored by Heritage Action, is a perfect 100 percent, compared to Rubio’s 86 percent

Cruz’s rapid assent has been compared to that of Barack Obama, who as a freshman senator went out of his way to endear himself to his party’s base and position himself to run for higher office in the future. “It’s obvious that he came here with a very different approach, to elevate himself and propel himself to national aspirations,” a GOP strategist tells National Review Online. But Cruz has also become a powerful force within Congress, wielding considerable influence with conservatives in the House. His efforts have almost singlehandedly foiled House speaker John Boehner’s plans on multiple occasions.

In what some view as an effort to curry favor with the base, Rubio joined Cruz in the campaign to defund Obamacare, but he has played a conspicuously subdued role, to the point where it is easy to forget that he is involved at all. “No one can say that Marco Rubio is the face of the shutdown,” says a senior GOP aide. Of course, that might not be wholly a bad thing, given the extent to which Cruz has alienated members of his own party over the past few months.