• Biden wants to help Ukraine before he leaves office.
• Jake Sullivan told ABC News that Biden aims to help Ukraine "strengthen' its position.
• President-elect Trump has been skeptical of the level of US aid sent to Ukraine.

National security advisor Jake Sullivan on Sunday said President Joe Biden was doing what he could to "strengthen" Ukraine's position as the commander-in-chief prepares to leave office in just under two months.

Sullivan made the remarks on ABC's "This Week," telling chief Washington correspondent Jonathan Karl that Biden aims to continue advancing his foreign policy objectives — which includes cease-fire discussions between Israel and Hamas — even as President-elect Donald Trump is set to be sworn back into office on January 20.

"We are going to do everything in our power for these 50 days to get Ukraine all the tools we possibly can to strengthen their position on the battlefield so that they'll be stronger at the negotiating table," Sullivan said. "And President Biden directed me to oversee a massive surge in the military equipment that we are delivering to Ukraine so that we have spent every dollar that Congress has appropriated to us by the time that President Biden leaves office."

Last month, Biden greenlighted Ukraine's use of powerful US-supplied ATACMS long-range missiles to strike inside Russia.

Trump has expressed skepticism regarding the level of aid sent to Ukraine, which puts him at odds with Biden, who has been a staunch ally of Ukrainian President Volodymyr Zelenskyy as the country continues its fight against Russia.

"I've encouraged the Ukrainian team to engage the incoming team as well as to engage all of our allies and partners, because, again, on January 21, the war in Ukraine doesn't just go away," Sullivan told Karl. "Obviously, the new team will have its own policy, its own approach, and I can't speak to that, but what I can do is make sure that we put Ukraine in the best possible position when we hand off the baton."