Trump's choice of Vance as his Vice Presidential running mate may increase the possibility of US isolationism over Ukraine ie. little or no more US aid for Ukraine. A Trump win on November 5, 2024 may further lead to Trump "the Statesman" brokering a Russo-Ukraine "peace" treaty that favours Russia's possession of Ukraine. Trump has a track record in his first presidency of siding with Putin.
Yet there are some factors that may persuade a second Trump Administration to maintain aid to Ukraine:
1. The US State, Defense departments and intelligence community might remind Trump that the war is eroding Russian military and political power. The Ukraine war may be costing Russia about US$200 million/day and weakening Russia’s army and navy.
2. Western sanctions on Russian energy sales are leading to international energy scarcity, with consequent energy price rises and higher profits for US companies including their profits on exports to European countries. This boosts US Government revenue from taxation on US energy companies.
3. Another factor in Ukraine's favour is that the Russo-Ukraine war benefits US arms companies selling weapons and ammunition to the US Defense Department which then gifts these items to Ukraine.
4. More generally what is good for the US military-industrial complex is good for the US in terms of increased US national economic growth.