Brett McGurk is a CNN global affairs analyst who served in senior national security positions under Presidents George W. Bush, Barack Obama, Donald Trump and Joe Biden.

To appreciate the dramatic shift in President Donald Trump’s policy towards Ukraine, consider two scenes in the Oval Office, months apart:

On February 28, Trump berated Ukrainian President Volodymyr Zelensky in front of the global news media, declaring that he has “no cards” and effectively no choice but to sue for peace with Russia and largely on Russia’s terms. Shortly after that meeting, the United States announced a temporary pause on all military and intelligence support for Ukraine.

On July 14, Trump met with the secretary general of NATO, Mark Rutte, and announced significant new cards for Zelensky, in the form of billions of dollars in military equipment, including advanced anti-air systems, and new sanctions on Russia to go into effect 50 days from now if Russian President Vladimir Putin continues to prosecute the war.

These scenes bookmark a chapter of ineffective American diplomacy and the beginning of a new and more promising one: diplomacy backed by the leverage ultimately required to stop a war that Putin has otherwise demonstrated he intends to continue indefinitely.