President Donald Trump on Wednesday revived a nickname he used for Sen. Bernie Sanders during the 2016 campaign season: "Crazy Bernie."

A day after Sanders announced he's joining the 2020 race, Trump on Wednesday tweeted, " Crazy Bernie has just entered the race. I wish him well!"

Sanders responded to Trump in a sternly worded tweet, calling the president "a racist, a sexist, a xenophobe and a fraud."

Sen. Bernie Sanders of Vermont is apparently not a fan of President Donald Trump's revived nickname for him.

A day after Sanders announced he's joining the 2020 race, Trump on Wednesday tweeted, "Crazy Bernie has just entered the race. I wish him well!"

The president used this nickname for Sanders during the 2016 campaign season.

Sanders responded to the president in a tweet not long after.

"What's crazy is that we have a president who is a racist, a sexist, a xenophobe and a fraud," Sanders said. "We are going to bring people together and not only defeat Trump but transform the economic and political life of this country."

For the past several weeks, there was a great deal of speculation that Sanders would run for president again after a 2016 campaign that was unsuccessful but made the Vermont senator a household name.

Sanders on Tuesday confirmed his plans to run during an interview with Vermont Public Radio (VPR), slamming Trump in the process.

Read more: Bernie Sanders announces he's running for president again in 2020

"I think the current occupant of the White House is an embarrassment to our country," Sanders told VPR. "I think he is a pathological liar — every day, he is telling one lie or another.

"And it gives me no pleasure to say that, but I also think he is a racist, a sexist, a homophobe, a xenophobe — somebody who is gaining cheap political points by trying to pick on minorities, often undocumented immigrants," Sanders added.

Later in the day, as Trump spoke with reporters about Sanders' announcement, the president said, "Personally, I think he missed his time. But I like Bernie because he is one person that you know on trade, he sort of would agree on trade. I'm being very tough on trade. He was tough on trade. The problem is, he doesn't know what to do about it."

Trump also wished Sanders well and said it "will be interesting to see how he does."