(Reuters) - Former Vice President Joe Biden, a leading contender for the 2020 Democratic presidential nomination, said on Monday he would consider choosing a Republican running mate if he is the party’s nominee next year.

However, even as he raised the possibility of a Republican running mate while speaking to a crowd at a campaign event in Exeter, New Hampshire, Biden said, “But I can’t think of one right now.”

Biden has premised much of his presidential bid on appealing to moderate Democrats, independents and Republicans who have been alienated by President Donald Trump. On the campaign trail, Biden has regularly spoken about the need to work with Republicans in Congress should he prevail in the November 2020 general election.

In response to a question by an attendee at the event, Biden elaborated on his answer, contending that Trump’s party has not done enough to hold the president accountable. “There are some really decent Republicans that are out there still, but here’s the problem right now,” he said. “They’ve got to step up.”

Biden, 77, who served two terms as vice president to former President Barack Obama and spent 35 years in Congress, has been criticized by progressive Democrats who say he is out of touch with the party’s leftward drift and is not interested in reforming the U.S. political system.

Biden has previously said he would like to name a woman and/or a person of color as his running mate if he is the nominee.

National opinion polls continue to show Biden the favored choice among Democratic voters ahead of his more liberal rivals, U.S. Senators Bernie Sanders and Elizabeth Warren. Biden’s chief argument for his candidacy is that he is best positioned to beat Trump next year because he can appeal to centrist voters in key battleground states.

Past presidential nominees have flirted with the idea of crossing party lines. In 2008, the Republican pick, the late U.S. Senator John McCain, wanted his close friend U.S. Senator Joe Lieberman, a Democrat-turned-independent, on the ticket. But pressure within the party pushed McCain to make former Alaska Governor Sarah Palin his vice-presidential choice, a move that backfired and helped Obama win election.