Here's the bulk of what Sanders said (it's long, but important):
"At the end of the day, what is most important to me is to see that Donald Trump is not re-elected president, and I intend to do everything I can to make sure that doesn't happen.
"But if -- and this is an if -- if for the next year, year-and-a-half, going right into the heart of the election, all that the Congress is talking about is impeaching Trump and Trump, Trump, Trump, and Mueller, Mueller, Mueller, and we're not talking about health care, we're not talking about raising the minimum wage to a living wage, we're not talking about combating climate change, we're not talking about sexism and racism and homophobia, and all of the issues that concern ordinary Americans, what I worry about is that works to Trump's advantage."
Sanders went on to say that he supports the House conducting an investigation into some of the seemingly obstructive behaviors by Trump documented by Mueller and that, once that investigation concludes, he was open to reassessing.
https://www.cnn.com/2019/04/23/politics/bernie-sanders-impeachment-cnn-town-hall/index.html