U.S. President Joe Biden and Ukrainian President Volodymyr Zelenskyy will sign a bilateral security agreement at the G7 summit Thursday that will pledge long-term defense and security cooperation.

"We want to demonstrate that the U.S. supports the people of Ukraine, that we stand with them, and that we'll continue to help address their security needs, not just tomorrow but out into the future," national security adviser Jake Sullivan told reporters aboard Air Force on his way to the G7 summit site of Bari, Italy. "We'll be sending Russia a signal of our resolve."

A U.S. official tells me this is an "executive agreement," which means a future president could withdraw from it.

The possibility of a second Donald Trump presidency looms large over the summit -- Trump has not made clear whether he would continue to support Ukraine and has said he'd "encourage" Russia to attack NATO allies who don't contribute enough towards defense spending.

The official told me negotiations on this bilateral agreement started last fall, but the U.S. was not able to complete negotiations while waiting for Congress to pass the supplemental funding for Ukraine. Once that was passed, negotiations were accelerated.

The agreement states that the U.S. intends to work with Congress over the coming months to find a path to sustainable resources for Ukraine.

The agreement does not include any commitment to use U.S. forces to defend Ukraine. It will outline a vision of how the U.S. and its allies will work with Ukraine to strengthen its defenses and deter future aggression from Russia.

The pledge will be similar to bilateral agreements that Ukraine has already signed with more than a dozen other countries.

"If Vladimir Putin thinks he can outlast the coalition supporting Ukraine, he's wrong," Sullivan added. "He cannot just wait us out."

Zelenskyy and Biden will meet Thursday on the sidelines of the G7 and will hold a joint news conference.