The Democratic leadership in Congress has suggested it would protect the Republican House speaker, Mike Johnson, if he bucks his far-right colleagues and brings a stalled $60bn Ukraine military aid package to a vote, as a new poll shows public support for Ukraine is now fractured down party-political lines.

Hakeem Jeffries, the House minority leader, floated the offer in an interview with the New York Times, saying “a reasonable number” of Democrats would vote to save the Republican speaker if the Ukraine vote resulted in a Republican mutiny.

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Far-right members of Congress including Marjorie Taylor Greene have said they would seek to depose Johnson if he brings the foreign aid bill forward, threatening to send Republicans toward yet another protracted leadership crisis like the one that paralyzed the House under former speaker Kevin McCarthy.

Jeffries said that if Johnson were “to do the right thing”, there would be a “reasonable number of people” on the Democratic side “who will take the position that he should not fall as a result”. But Jeffries said he had not discussed the matter with Johnson, who has said Congress “must take care of America’s needs first”.

The political carrot was extended a day after Joe Biden and congressional leaders pushed Republicans to move the aid bill forward. Johnson later told reporters that they had been working in “good faith, around the clock every single day” on a spending deal.

Johnson also said the legislative body was “actively pursuing and investigating all the various options” for passing Ukraine aid, but “the first priority of the country is our border”.

A new poll showed that US adults have become politically split down party lines over giving more military aid to Ukraine, which the country says it desperately needs to fend off Russian advances.

A majority of Republican voters (55%) said the US was spending too much on Ukraine, according to the Associated Press-NORC Center for Public Affairs research, while support for Ukraine has grown among Democrats.

Democrats, meanwhile, registered increasing support for aid to Ukraine, with about 40% saying the US was spending “too little” on it – a sharp rise from 17% in November.

The survey shows that Russia’s Vladimir Putin remains unpopular with Americans, but that the depth of his unpopularity is similarly shaded – with roughly nine in 10 Democrats compared with three-quarters of Republicans holding the view.

Only about four in 10 adults polled had a favorable opinion of the Ukrainian president, Volodymyr Zelenskiy.

A majority – including 52% of Republicans – said they supported the spirit of Article 5 of the Nato military alliance that an attack on one Nato country is an attack on all, while about 60% said they would support US forces becoming involved if a Russia attacked a Nato member.

In a state of the union speech on Thursday, Vladimir Putin described claims that Russia intended to attack Europe as “nonsense”.

But the Russian president added that any increase in western support for Ukraine “risks a conflict using nuclear weapons, which means the destruction of all civilisation”.