After the release of 3 American citizens from Russian captivity on Thursday, journalists grilled 46 about his motivations behind coordinating the act of diplomacy. As one journalist asked ... was it important for Biden to pull off the deal under his administration -- especially since he ended his reelection bid??

Biden seemed to laugh off the question, as he told reporters he's still got plenty of work to do for the next few months.

He quipped ... "You're stuck with me as president for a while, kid. There's no way out. You've got me for at least another 100 days or so."

The prez's comments come amid calls from some Republicans, who feel Biden should step down now. Their argument -- if he can't run a political campaign, he can't run the country.

Biden clearly feels differently. He's been present and loud over the last day or so, touting his prisoner trade deal with Russia.