That's what happened to Carson. He rose a few months into the race, taking the lead in Iowa and tying Donald Trump nationally. By early November, he started to slip in Iowa — and collapsed as the Paris attacks in the middle of that month turned voters' attention to foreign policy, where they already saw him as weak.
By the end of the year, the Republican field in Iowa looked exactly as they'd eventually finish, with the exception of Marco Rubio, who didn't surge until shortly before voting began.
You can see that the beneficiary of Carson's collapse was largely Cruz; the two criss-crossed in Iowa right at the beginning of December. Carson's support fell. Cruz's rose.
As the caucus approached, Trump's attacks on Cruz appeared to weaken the Texas senator, and Trump passed him in the polls at the end of January. Carson, though, kept slipping. His average in the polls Jan. 1 was 9.2. On Jan. 15, it was 9. By Jan. 30, it was 8.8. And in the last polling average from Real Clear Politics, on Jan. 31, Carson was at 7.7.
On that day, Carson appeared on Fox News and insisted that he'd go on to New Hampshire after Iowa, no matter what. He put it more strongly than that; asked whether there was any scenario where he wouldn't go on to New Hampshire, Carson replied, "If I die."
By noon the next day, Feb. 1, the day of the caucus, Carson was apparently either dead or had changed his mind. At about 1 p.m., the Columbia State reported that Carson was skipping New Hampshire and focusing instead on South Carolina. "New Hampshire tends to be a little more liberal state, and I am not really going to resonate with liberals very well, which is okay," Carson said.
At 6:43 p.m. Central time, 15 minutes before the caucuses started, CNN reported that Carson would leave Iowa and take some time off in Florida — not South Carolina — before heading back to Washington for an event. Carson's campaign also told CNN that the candidate would address supporters at 9:15 p.m. Central time — which might even be before caucusing ended in some locations.
The campaign of Ted Cruz jumped on the news, sending out an email saying that Carson was taking time off after Iowa and "making a big announcement" next week. Trump tweeted images of the email and a now-deleted tweet from a Cruz staffer Wednesday as part of his effort to show that Cruz committed "fraud" and "stole" the Iowa caucus.
There were other anecdotal mentions of people at caucus sites saying that Cruz supporters were telling Carson backers that the doctor was dropping out — including one Facebook post saying that a supporter said it at a caucus attended by Carson's wife. (She reportedly denied it.)
When he thanked supporters in a statement Monday night, Carson referred to his campaign having "survived the lies and dirty tricks from opponents who profess to detest the games of the political class, but in reality are masters at it."
"Even tonight," he wrote, "my opponents resorted to political tricks by tweeting, texting and telling precinct captains to announce that I had suspended my campaign — in some cases asking caucus-goers to change their votes." That's the argument that Trump seized on in an effort to undermine Cruz's win.
There's no question that Cruz's staffers shouldn't have emailed any suggestion that Carson was dropping out when they didn't know that he was; Cruz's campaign apologized for doing so.
But fault also lies with Carson's campaign for giving out a number of different messages in the 24 hours leading up to the caucuses. On Sunday, he was full steam ahead. On Monday, he bailed on New Hampshire, and then revealed to CNN that he was taking time off from the campaign trail. He's not a polished politician, but it's hard to think that the response wasn't predictable. When a candidate says he's "taking time off," that is not a candidate who is poised for victory.
When assessing Cruz's sharing a deliberately misleading version of Carson's story, though, it's worth trying to figure out what damage was done. Cruz and Carson shared a base of support, as we saw at the end of the year. But for Cruz to have moved into first place by siphoning off support from Cruz, he'd have had to have peeled away about 6,200 votes — or a quarter of Carson's support. That's unlikely.
What's more telling, though, is that Carson's support actually increased from the last polling average in Iowa.
On Jan. 31, he was at 7.7 percent. He finished at 9.3 — a higher percentage than he'd seen in the polling average since the calendar turned to 2016. It's hard to see how he could have outperformed his polling and lost a lot of his support thanks to Cruz's machinations. Carson had more votes than every sitting and former governor in the race, combined. This was a fourth-place finish, but Carson still did better than one might have expected.
Three months ago, Ben Carson could look ahead and see, if not the presidency, then an historic win in the Iowa caucuses. Then, as his party's new front-runner, he had to endure the examination of his record that comes with that position — and he handled it relatively poorly. Voters changed their minds, and his polling in Iowa suffered as a result.
There's a sense in which Carson's complaints about Cruz stealing his votes is entirely accurate. Cruz did steal his votes — back in November. That's the point at which Carson lost Iowa, and the point at which he should have complained. Everything else is sour grapes.