Hillary Clinton says Sanders would not be 'strongest nominee against Trump'

Bernie Sanders would not be the Democrats’ “strongest nominee against Donald Trump”, Hillary Clinton said – as new polling of battleground states backed her up.

Related: Bernie Sanders returns to Michigan in need of 2016 repeat

Results from Firehouse Strategies (a firm founded by Republicans) and 0ptimus found that in Michigan, Pennsylvania and Wisconsin, since December, “Trump’s lead has dropped considerably against both Vice-President [Joe] Biden and Senator Bernie Sanders”.

According to the survey, in Michigan – which holds its Democratic primary on Tuesday and where Biden has established a lead over Sanders – Trump leads Biden by two points and Sanders by seven. In Pennsylvania the lead is one point over Biden and four over Sanders and in Wisconsin it is two points and six.

In general, such head-to-head polling in swing states produces close match-ups.

Clinton lost Michigan, Pennsylvania and Wisconsin to Trump in 2016, as the Republican’s success in Democratic strongholds swept him to victory in the electoral college despite losing the popular vote by nearly 3m ballots.

Clinton told CNN on Sunday she was not endorsing anyone yet – given her harsh comments about Sanders in the recent past, the point was almost moot – but added: “I think what Joe’s victories on Super Tuesday showed is that he is building the kind of coalition that I had basically.

“It’s a broad-based coalition. [In 2016] I finished, you know, most of the work I needed to do for the nomination on Super Tuesday, and then it kind of lingered on. And I think Joe is on track to doing exactly the same thing: putting together a coalition of voters who are energised.”

The former first lady, senator and secretary of state also said she hoped Sanders would back Biden if the former vice-president wins the nomination.

“I hope so because his failure and the behaviour of a lot of his top aides, and certainly many of his supporters – up to the convention, at the convention, and even up to election day was not helpful,” Clinton said of 2016.

“I had thought we would unify, that’s what we’d always done before and that’s what I expected. I certainly tried to do that when I ran against Barack Obama [in 2008] and worked very hard for him.”

Clinton told CNN she would “support the nominee of the Democratic party” but did not know if Sanders would ask her to campaign for him if it was him.

As the former Maryland governor and 2016 candidate Martin O’Malley made clear to the Guardian last month, Sanders’ supposed failure to back Clinton properly in 2016 is a running sore with Democratic party insiders.

In return, Sanders, who sits in the Senate as an independent, continues to campaign as an outsider, a wedge point Trump continues to seek to exploit.

On Monday, in news sure to rile Sanders supporters, Axios reported that some party insiders, or “Biden confidants”, are discussing cabinet appointments.

The report mentioned the usual suspects for vice-president, including Senator Kamala Harris, who endorsed Biden on Sunday, and Stacey Abrams of Georgia. Senator Cory Booker of New Jersey, another leading African American figure, announced his endorsement of Biden on Monday.

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According to Axios, John Kerry, who succeeded Clinton as secretary of state under Obama, “would love to take a new cabinet position devoted to climate change, or might even accept a curtain call to return as secretary of state”.

The report also named the billionaire former New York mayor and Democratic candidate Mike Bloomberg as a possibility to lead the World Bank and another former challenger, the progressive Massachusetts senator Elizabeth Warren, as a possible treasury secretary who might “help unite the party”.

Axio cited “campaign officials” as saying “the name game isn’t where Biden’s head is – he knows he has major primary and general-election fights ahead”.

But it also pointed to “sudden optimism around his candidacy”.

The Biden campaign reacted strongly, a spokesperson saying the Axios report was “like fantasy football for politics” and adding: “It is laughable speculation and should only be treated as such.”