President Donald Trump took aim at Democratic presidential contender Beto O’Rourke in a new tweet released this week.

On Wednesday morning, Trump tweeted regarding O’Rourke’s proposal for a mandatory “buy back” of AR-15 and AK-47 firearms, if elected President. In the tweet, Trump called El Paso’s O’Rourke a “dummy,” and also criticized Democrats for their gun control proposals.

“Dummy Beto made it much harder to make a deal,” Trump said. “Convinced many that Dems just want to take your guns away. Will continue forward!”

O’Rourke responded a few hours later to Trump’s tweet, saying the President is showing “cowardice” in his position.

“To be clear: We will buy back every single assault weapon,” O’Rourke said. “We‘ll also license every gun & do a background check on every buyer. That’s what the American people want—and deserve. The only thing stopping us from ending this epidemic is you & your cowardice. Do the right thing.”