The Cruz campaign is built on the premise that he can consolidate the Right and that doing so is sufficient to win a general election. There is no doubt that he has made progress in uniting the base. Social conservatives, led by Tony Perkins of the Family Research Council, have coalesced around Cruz, whose chief rivals in that camp — former Texas governor Rick Perry, Wisconsin governor Scott Walker, Louisiana governor Bobby Jindal — have dropped out of the race already.

Cruz has money (nearly $14 million on hand at the beginning of October, and much more stashed away in a cluster of super PACs) and momentum, and he has invested heavily in fieldwork. In Iowa, New Hampshire, South Carolina, and Nevada, his team boasts volunteer county chairmen in all 171 counties. It has volunteer coordinators in all 163 congressional districts in the first 24 nominating states. He has focused particular attention on the first-ever “SEC primary” (nicknamed after the regional football conference) on March 1, which includes several southern states flush with Evangelicals who have never before had the opportunity to influence the nomination process.

But some question whether his is a winning general-election strategy. “His argument is, not only do you just need Republicans to win the general, but you just need half of Republicans,” says a Republican strategist familiar with Cruz’s thinking. “It’s not terribly controversial to say we need not just Republicans, but some non-Republicans, too.”

Rubio’s theory is that a conservative can unite the Right, but that the nominee can and must attract the party’s moderates, and ultimately some Democrats, to the conservative cause. Meanwhile, it has come as a surprise to many that it is Rubio, rather than Walker, Jindal, or Perry — or Mike Huckabee or Rick Santorum — who is evidently emerging as Cruz’s chief impediment to unifying the party’s right flank.

Rubio’s advisers insist they are not ceding an inch to Cruz when it comes to chasing conservative voters, even as Rubio has become a leading establishment candidate, earning the support of top party donors, including hedge-fund billionaires Paul Singer, Cliff Asness, and Ken Griffin. “We are running in the conservative lane,” says a top Rubio adviser.