Joe Biden is running in a historically large Democratic primary, in which he has slipped from the top of some polls. His fundraising has dropped and some say he may be too moderate or too old to fight Donald Trump next year.

But the former vice-president insisted on Saturday that some who back him think “it’s a general election, me versus Trump” and claimed: “Trump doesn’t want to face me.”

Biden spoke to the Associated Press before a town hall in Florence, South Carolina, the first southern state to vote.

The former Delaware senator leads the realclearpolitics.com national polling average by six points from Elizabeth Warren and maintains a healthy lead in South Carolina itself. But the Massachusetts senator has been surging elsewhere, leading in Iowa and New Hampshire, the first two states to vote.

“She doesn’t affect my strategy, period,” Biden told the AP. “And I’m not being facetious. I think she’s a fine person, a good candidate, but I didn’t get involved in deciding to run because of polling or a particular strategy.”

It is not surprising that those who are dedicated to defeating Donald Trump are organizing in every way permitted Kate Bedingfield

He added: “There’s two things we know for certain. One, Vladimir Putin doesn’t want me to be president, according to Facebook taking down the Russian ads going after me. And two, surely Trump doesn’t want to face me.”

Trump’s attempts to force Ukraine to investigate Biden are at the heart of the impeachment inquiry.

Biden had said he would not accept support from Super Pacs, which can raise money for candidates but cannot coordinate with them.

But on Thursday his deputy campaign manager, Kate Bedingfield, said that while he would still “push to remove private money from our federal elections … in this time of crisis in our politics, it is not surprising that those who are dedicated to defeating Donald Trump are organizing in every way permitted by current law to bring an end to his disastrous presidency.”

Earlier this month, Biden reported $15.2m raised in the third quarter. That put him fourth in the race, behind the Vermont senator Bernie Sanders ($25.3m), Warren ($24.6m) and Pete Buttigieg, the 37-year-old mayor of South Bend, Indiana, who raised $19.1m and has also surged in Iowa, attracting national headlines.

On Saturday, Biden said: “What I’m told is, there are people out there who want to take these ads on, take him on now, because it’s a general election, me versus Trump, in their minds right now. But I’ve had no conversations with them.”

It has been reported that some donors, faced with Biden’s stumbles and Warren’s rise as a force for progressive policies, are looking to the former New York mayor and media billionaire Michael Bloomberg as a late entrant in the ideological centre.

Biden insisted he would do “very well” in Iowa and New Hampshire but said losses wouldn’t hurt him and South Carolina could “catapult” him to success across the south.

The former vice-president is 76. Sanders is 78 and recently suffered a heart attack. Asked if age mattered, Biden said: “Right now it’s a legitimate question to ask … Right now, my age has brought with it a significant amount of experience in government and hopefully wisdom and some sound judgment.”

Asked if he would pledge to only serve one term, Biden said: “I feel good and all I can say is, watch me, you’ll see. It doesn’t mean I would run a second term. I’m not going to make that judgment at this moment.”