(CNN) Outgoing Indiana Democratic Sen. Joe Donnelly said Democrats need to be careful in promoting too many progressive ideas in red states like his because they'll "start losing the people in my state."

"Medicare-for-all" is a progressive stance that some Democrats worry could alienate Midwestern voters from the party going into the 2020 presidential election. It has become popular thanks to liberal leaders like Vermont Sen. Bernie Sanders.

When asked by CNN's Dana Bash on "The Lead With Jake Tapper" if Democrats could be viable without appealing to interior state votes, Donnelly replied, "I don't know how you do that."

Donnelly said that during President Donald Trump's visits to Indiana in the weeks before the midterms -- in which Donnelly lost his seat -- the President made not voting for Republicans seem like a personal betrayal by voters.

"We have not made enough of a connection ... that the people of my state understand culturally, we (Democrats) want to make sure you succeed," he said.

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