United States President Joe Biden will try to convince President-elect Donald Trump not to pull support from Ukraine when he takes office, the outgoing president’s national security adviser has said.

Biden will make his pitch to Trump, who has repeatedly bashed US aid to Ukraine, when the two meet on Wednesday for a White House transition meeting, Jake Sullivan said in an interview with the CBS News programme Face the Nation on Sunday.

“President Biden will have the opportunity over the next 70 days to make the case to the Congress and to the incoming administration that the United States should not walk away from Ukraine, that walking away from Ukraine means more instability in Europe,” Sullivan said.

“Biden will make the case that we do need ongoing resources for Ukraine beyond the end of his term,” he added.

The war in Ukraine highlights a stark foreign policy divide between Biden and Trump.

Under Biden, the US government has committed some $174bn in aid to Ukraine as it battles invading Russian forces, with the US president lobbying other NATO allies to keep up support as well.

Trump, however, has repeatedly slammed aid to Ukraine and said he would end its war with Russia “in a day”. To do so, he has suggested Ukraine may have to cede territory in a peace deal, something the Ukrainians reject and Biden has never suggested.

According to a Washington Post report on Sunday, Trump spoke to Russian President Vladimir Putin on Thursday, urging him not to escalate the war in Ukraine.

While Trump has not gone into detail on how he plans to end the 2.5-year war, his incoming Vice President JD Vance has offered a rough vision.

“What it probably looks like is the current line of demarcation between Russia and Ukraine, that becomes like a demilitarised zone,” Vance said on the Shawn Ryan Show podcast in September.

“Ukraine retains its independent sovereignty, Russia gets the guarantee of neutrality from Ukraine – it doesn’t join NATO, it doesn’t join some of these allied institutions. That is what the deal is ultimately going to look something like,” he said.

Fearing waning support from the US under Trump, the Ukrainians and European NATO members have been scrambling to reach out to the president-elect.

Ukraine’s President Volodymyr Zelenskyy, in a message congratulating Trump on his election victory, wrote: “I appreciate President Trump’s commitment to the ‘peace through strength’ approach in global affairs. This is exactly the principle that can practically bring just peace in Ukraine closer.”

He added: “We rely on continued strong bipartisan support for Ukraine in the United States.”

‘Strongest possible position’

Sullivan said one of the Biden administration’s main goals in its remaining months, will be “to put Ukraine in the strongest possible position on the battlefield so that it is ultimately in the strongest possible position at the negotiating table”.

As part of this effort, the White House is rushing aid to Ukraine, with plans to spend its remaining $6bn of Ukraine funding before Trump’s presidential inauguration in January, according to Sullivan.

Sullivan said Trump and Biden will have the opportunity to review Washington’s stance on Ukraine, along with other foreign policy issues, and discuss how Trump plans to tackle them during their meeting on Wednesday.

“The president will have the chance to explain to President Trump how he sees things, where they stand, and talk to President Trump about how President Trump is thinking about taking on these issues when he takes office,” he said.

The drawn-out war in Ukraine is entering what some officials say could be its final act after Moscow’s forces advanced at the fastest pace since the early days of the war.

Any fresh attempt to end the war is likely to involve peace talks of some kind, which have not been held since the early months of the war.