CNN  — 

West Virginia Sen. Joe Manchin on Monday said Senate Republicans blocking a border and foreign aid bill earlier this month was the “biggest part” of his decision to not run for president after he had previously weighed a third-party campaign.

The retiring Democratic lawmaker told CNN’s Kaitlan Collins that watching the bipartisan bill collapse in the Senate “was the biggest part of the decision because I came to the final conclusion – I always believed that we could legislate through a crisis, we’d come together for a crisis. Well, guess what, we have a crisis. The border is a crisis.”

Manchin’s explanation follows closely on the heels of his Friday announcement that he “will not be involved in a presidential run” and comes as Congress remains gridlocked. Top House Republicans are refusing to support a new foreign aid package after Senate Republicans pulled an about-face on the previous combined border and aid legislation that faced opposition from House GOP leadership and former President Donald Trump.

The failed procedural vote two weeks ago was a rebuke from Senate Republicans of a deal that would have enacted restrictive border measures and was crafted in part by one of their own members – James Lankford of Oklahoma, who Manchin referred to as the “most decent, honorable person and conservative in the entire Senate.”

“I saw my friends walk away when they were determined to pass a border security, and they were on board three days before that. And with Donald Trump coming as hard as he came at them, they cower down and walked away. I said, ‘We’re not fixing anything in Washington,’” Manchin told Collins on “The Source.”

Manchin, a centrist who has often been at odds with members of his party, had set a deadline of this spring to determine whether he would make a run for the White House, potentially on the No Labels ticket. But he announced on Friday that he was pulling the plug to focus on a new group, Americans Together, which promotes moderate politics.

On Monday, he again refused to endorse Former President Joe Biden and criticized the president for being too liberal, while adding that he would not be part of any effort that would help Trump return to the White House.

“I’m not endorsing anybody right now. We’re gonna see what all happens. We’ve still got plenty of time here. I’m gonna do everything I can to help move them back to the middle and show them where the strength of this country lies, where the voting bloc of the country lies,” Manchin said.

Pushed by Collins on what he would do if the presidential ticket is again Biden versus Trump, Manchin said, “We’ll just have to see what happens.”

“That’s a long time before that happens. Right now there might be other people getting in, there’re still independents, you might have still a third party run from No Labels, and we’ll just see what opportunities and what type of options you have,” he said.

CNN’s Edward-Isaac Dovere contributed to this report.