Biden spoke to Markey supporters at a Washington, D.C., fundraiser hosted by former Vice President Gore and Vicki Kennedy, widow of former Sen. Ted Kennedy (D-Mass.) that brought in about $250,000, according to Markey's campaign.
The congressman himself did not attend the fundraiser, spending his night instead sparring with Republican Gabriel Gomez in their second debate.
Biden praised Markey effusively and said he could have a "potentially profound impact on the issues of the day" if elected to the Senate. Biden said "a single vote" could be pivotal in raising the debt ceiling and passing immigration reform.
“I’ve been doing this a long time. I’ve seen a lot of people come and go,” Biden said. “But few have the quality of character, and intellect, and emotional IQ that Ed Markey has."
He continued to warn, however, that supporters shouldn't "underestimate this race," noting that the timeframe of the special election meant many voters were likely tuned out.
“I know I’m preaching to the choir,” Biden said after praising Markey. “But I’ve gotta tell ya. Don’t underestimate this race. Ed’s ahead, Ed should win. But this is a strange moment. There’s not a lot of people paying attention.”
And though Biden didn't mention Markey's opponent by name, he criticized the GOP, saying the nation didn’t need another Republican Senator in Washington.
Biden said there is a "chasm" between the two parties.
“I’m being straight about this," he said. "This is not your father’s Republican Party. It really is a fundamentally different party. There’s never been as much distance, at least since I’ve been alive, distance between where the mainstream of the Republican congressional party is and the Democratic Party is. It’s a chasm. It’s a gigantic chasm.”
Biden suggested Republicans in the Senate were beholden to Sens. Ted Cruz (R-Texas) and Rand Paul (R-Ky.) on gun control, saying that he called 17 senators out on their votes against gun-control legislation and all said they were concerned the two senators would campaign against them.
“Not one of them offered an explanation on the merits of why they couldn’t vote for the background check. But almost to a person, they said, ‘I don’t want to take on Ted Cruz. I don’t want to take on Rand Paul. They’ll be in my district,' " he said.
Markey has led Gomez throughout the race but many polls show him up by only single digits, stoking Democratic worries that the party could suffer an upset similar to the one that brought former Sen. Scott Brown (R) to the Senate in 2010.
To prevent such an outcome, Democrats have rolled out some of their biggest names to campaign for Markey, including first lady Michelle Obama, Biden and on Wednesday, Obama, who will stump for him in Massachusetts.