I asked everyone I talked to at the Sheraton whether they felt Trump had made any mistakes in the campaign, like deciding not to attend last Thursday’s Republican debate. Most felt Trump had made the right call; they weren’t in the mood to second-guess their candidate. But in light of the caucus results, the debate decision looms as a critical error in judgment for Trump.

In the days leading up to the voting , when I talked to voters on the fence between candidates — people who could possibly be persuaded to support Trump — one thing became clear: everybody watched the debate. It was the only debate held in Iowa, and it took place in the final days of the campaign, when voters who had been reluctant to pay attention months earlier had finally become interested and involved. They all tuned in. And Trump wasn’t there.

“That was the one thing that I thought was a clear mistake,” Republican blogger Craig Robinson, a former political director of the state GOP, said in a phone conversation Monday afternoon. With that one decision, Trump undermined a lot of the work he had done in the previous months.

The debate decision showed that Trump’s political instincts could be wrong. But the caucus loss could point to even more serious problems ahead for Trump.