Just before the New Hampshire vote, Stuart Stevens complained that Trump was being aided by a common delusion among his rivals:

Under the “lane theory” of politics, candidates are best served only competing for those voters who meet certain, very specific qualifications. There is an “establishment” lane and an “evangelical lane,” a “liberty voter” lane and so on. This all sounds interesting and is a convenient way to try to impose order on a chaotic process but it has one fundamental flaw: There are no lanes. The electorate consists of voters drawn in many different directions simultaneously with conflicting motivations and values. There are plenty of voters who have “establishment, evangelical, liberty” elements—and more—within them and that gives a candidate more opportunity to appeal to their vote, not less.
The result of this crackpot “lane theory” is the assumption that Donald Trump is in his own lane. . . and those voters are inaccessible to serious candidates in a different lane. Therefore the serious candidates are best served attacking each other rather than going after the candidate with the most votes. If that sounds nutty, well, it is.

I don’t think the lane theory is quite as bankrupt as Stevens suggests. There is an important sense in which Kasich, Bush, and Rubio will be competing with one another in South Carolina. The two of them who place lowest will be in very bad shape, however Cruz and Trump perform. Their campaigns may well be over. That’s because there are voters, donors, and party leaders who will want to winnow the non-Trump, non-Cruz field down to one.

In South Carolina as in Iowa, Cruz will have a greater incentive than the other candidates to attack Trump. Bush, Kasich, and Rubio will continue to have more reason to attack one another than to take him on. But to have a shot at the nomination, they may need to start weakening Trump too. It may even help them in South Carolina, since, as Stevens rightly suggests, Trump is currently winning some of their potential voters. Anti-Trump Republicans have been tearing their hair out about the free ride Trump got in New Hampshire, but it will end soon enough.

(disclosure)