Former Democrat Chicago Mayor Rahm Emanuel penned a memo aimed at all of the 2020 Democrat presidential hopefuls, urging them to go beyond Twitter in delivering a message that resonates with the American people.

“There’s a reason Trump gleefully tweeted ‘That’s the end of that race!’ during the first debate: Too often, you succumbed to chasing plaudits on Twitter, which closed the door on swing voters in Wisconsin, Michigan, Pennsylvania, and Ohio,” Emanuel wrote in an op-ed published Monday on Medium.

“If you win the nomination in a way that forecloses a path to victory in the general election, we will lose, and your name will go down in infamy,” he wrote, saying that he hopes the candidates could take that message to heart in the Detroit debates this week.

Emanuel advised the 2020 hopefuls not to repeat many of the pitfalls that took place in Miami during the first set of debates.

“Before our party promises health care coverage to undocumented immigrants — a position not even Ted Kennedy took — let’s help the more than 30 million Americans who are a single illness away from financial ruin,” he wrote.

Emanuel, a two-term mayor who opted not to seek a third term, has sounded off on many national issues.

The former chief of staff for former President Barack Obama said in December after the Democrats won the House of Representatives that Democrats need to spend the next two years “dividing” President Donald Trump and the GOP and endorsed then-House Minority Leader Nancy Pelosi (D-CA) for speaker.