New York City Mayor Bill de Blasio ended his campaign for president on Friday morning, acknowledging that he was unable to successfully pitch his progressive ideas to the Democratic electorate.

"I feel like I have contributed all I can to this primary election. It's clearly not my time, so I'm going to end my presidential campaign," de Blasio said on MSNBC's Morning Joe.

De Blasio's exit makes him the sixth candidate to drop out of the field, bringing the total number of Democrats seeking the nomination to 19.

Former Texas Rep. Beto O'Rourke gave a staunch defense of his gun control plan during Thursday's Democratic presidential primary debate, saying that as president, he would prioritize mandatory buybacks of assault-style weapons.

Quoting the candidate's past comment about selling back AR-15s and AK-47s, moderator David Muir asked O'Rourke: "Are you proposing taking away their guns? And how would this work?"

O'Rourke answered, "Hell, yes, we're going to take your AR-15, your AK-47."

Here's more of what he said:

The fate of the filibuster — a 60-vote threshold for most legislation in the U.S. Senate — is again an issue of controversy among Democratic presidential candidates.

Massachusetts Sen. Elizabeth Warren said the supermajority requirement is preventing Congress from passing popular bills — such as a background check bill.