DES MOINES, Iowa — Supporters of President Trump don’t agree with Bernie Sanders on almost anything, or even like him much, but they see him as a tough general election foe.

Thousands came out to see the president on Thursday evening, just four days before the Democrats hold their caucuses, the party’s first nominating contests of 2020. As they cheered on Trump at Drake University’s arena and weathered below-freezing temperatures to watch Trump’s remarks on a television outside, one lingering factor kept them unnerved: Sanders, the Vermont senator.