It is Ukraine that is being occupied. It is Ukrainians that are being killed, raped, and forcibly removed. The US providing military aid to Ukraine doesn't give us control over their agency.
It isn't like Ukraine doesn't want peace. They were the one that was attacked. It is Putin that doesn't want peace. It is Putin that refused initial negotiations. It is Putin that acted in bad faith in the peace process. It is Putin that can always leave Ukraine and end this war.
Part of why the Progressive Caucus' letter was so naive was that they ignored all of this.
Amash offers no constructive ideas here. Just empty signalling.