Former United States president Donald Trump is reportedly urging partymates to oppose a deal between Republicans and Democrats in the Senate tying military assistance for Ukraine with money to counter immigration at the Mexican border.

US media reported that Trump opposes the deal to deny Democratic President Joe Biden a political win ahead of November’s election.

A poll rematch between Biden and Trump looms as the two have virtually won the presidential nomination race of their respective party.

Republican Senate Minority Leader Mitch McConnell reportedly told senators in a closed-door meeting on Wednesday that they should not “undermine” Trump, US media outlets reported.

Discussions were continuing Thursday with the White House urging senators to reach a deal.

White House Deputy Press Secretary Olivia Dalton said Biden’s administration had been working in “good faith” with Republicans to reach a deal, including a meeting with the president last week.

“We’re going to continue to work on that in good faith, and we hope that Republicans will remain at the table so we can do that,” she told reporters aboard Air Force One.

US National Security Council spokesperson John Kirby said Russia was “watching closely” to see whether Washington would continue to deliver support for Ukraine.

Money for US aid to Ukraine has run out due to the lack of an agreement in Congress, leaving the key US ally short of ammunition as it tries to fight off Russia’s invasion.

Trump has made immigration a major plank of his campaign for a return to the White House, and has long opposed more aid for Ukraine.

Trump was impeached while in office after linking Ukraine self-defense aid to demands for politically damaging material on Biden and his son’s business deals there.