President Donald Trump lost Colorado by 5 percentage points in 2016, and he’s on pace to lose it by more this year. His most recent approval rating there was 39%, according to Morning Consult.

His unpopularity creates a problem for Cory Gardner, a first-term Republican senator from Colorado, who will be running for reelection this year — which makes Gardner’s behavior during the impeachment trial especially striking. Rather than act as the senator he is, with his own power to shape events, Gardner has served as a Trump loyalist.

Gardner has not expressed skepticism about the obvious lies Trump’s lawyers are telling. Gardner doesn’t seem concerned about Trump perverting foreign policy for his own personal interests. And Gardner has shown no interest in hearing all the relevant evidence by calling witnesses to testify.

We now know that John Bolton, Trump’s former national security adviser, heard the president demand the precise quid pro quo that he has since denied. For Bolton to be called to testify, however, at least four Republican senators would have to join with the 47 Democrats and independents to create a majority.

Gardner would seem to be an obvious candidate for one of those four. Yet media coverage typically overlooks Gardner. He’s simply assumed to be a Trump defender.

Gardner is making a bet. Even though many of his constituents — most, perhaps — believe that Trump has violated his oath of office, Gardner has evidently decided that he can safely ignore them.

In November, Colorado’s voters will get a chance to prove him wrong.

For more

— Gardner recently dodged questions from a Denver television station about whether he would vote to call witnesses. He also refused to answer questions from The Denver Post about whether the Senate would call witnesses. “Silence has become the norm for Gardner on the topic of impeachment,” The Washington Post’s Justin Wingerter wrote.

— In October, Gardner issued a statement calling the House impeachment process a political circus. “I hope,” he said, “that everyone supports a fair and transparent process.”

— “Mr. Gardner’s invisibility — he hasn’t held a town hall-style meeting in two years — is also pragmatic, a means of avoiding questions about his ties to the divisive president, especially as the Senate impeachment trial nears,” The Times’s Elaina Plott wrote this month.

— Other vulnerable Senate Republicans who have shown little sign of supporting a full hearing of the evidence include Martha McSally of Arizona, Thom Tillis of North Carolina and Joni Ernst of Iowa.