WASHINGTON (BLOOMBERG) - Democratic presidential candidate Bernie Sanders said his competitor, Joe Biden, could beat President Donald Trump in November, but added that he would be the stronger general-election candidate.

"We are the stronger campaign to defeat Donald Trump but you have not heard me say that I think that Biden cannot defeat Trump," Sanders told reporters in Phoenix, Arizona, as he boarded a plane to campaign in Michigan.

The question for voters, he added, is "which campaign is best positioned to defeat" the president.

Sanders said he intended to highlight the differences between his record and Biden's. He listed policies that he opposed and Biden supported, such as "Don't Ask, Don't Tell," the policy that barred openly gay people from serving in the US military, and the Hyde Amendment, which barred the use of federal funds to pay for abortion.

The Vermont senator also attacked Biden for his 1996 vote, as a senator representing Delaware, in favour of the Defence of Marriage Act, which defined marriage as between a man and a woman.

"The point here is not just to look back 20 years, not just to look at consistency, it is to look at which candidate had the guts to cast difficult votes," Sanders said.

"Because they were the right votes, even though one knew that they would be unpopular. That is the issue."

PAST POSITIONS

Sanders also renewed his criticism of Biden for past support of trade deals such as the North American Free Trade Agreement, which he said had been "disastrous" for states like Michigan. Trump, he said, was likely to attack the former vice-president on the same grounds.

"In terms of the coming general election we don't have to predict what Donald Trump will say about Joe Biden, because he's already making those attacks," Sanders said.

After losing 10 of 14 states on Super Tuesday, Sanders is redirecting his efforts towards Michigan, the biggest prize in terms of delegates of the six states holding Democratic nominating contests on March 10.

Sanders had a narrow upset victory over Hillary Clinton in the state's 2016 Democratic primary.

Michigan will be critical to his ability to catch up to Biden, who overtook him in delegates after Super Tuesday.

He said he had not spoken to Biden since the contest essentially became a two-candidate race.

Sanders added that he would support Biden if the former vice-president became the nominee, and that Biden would return the favour.

"I have said, from day one when announced, that I will support the Democratic nominee. And I will support Joe Biden," Sanders said.

"Joe Biden has indicated he will support the Democratic nominee and support Bernie Sanders."