Democratic U-S Senator Ed Markey of Massachusetts, says he’ll never understand why many Republican voters view presidential candidate Donald Trump so favorably.

“I will just have to leave that to them,” Markey says. “They’re experts in selecting their own candidates and I don’t think that we, as Democrats, should interfere with that process. I think they’re doing a good job right now in their support for Donald Trump,” Markey said to laughter at a press conference in Springfield Tuesday.

Markey says he has not yet made a formal endorsement in the 2016 Democratic primary. But he offered positive words for Hillary Clinton, saying if she is the nominee, she would be tough for the Republicans to defeat.