. Carve off the eastern side that's populated by ethnic Russians and give Ukrainians guarantees we'll come to their aid if Russia ever invades again.
we already gave that guarantee before.
Budapest Memorandum
Signed in 1994, this agreement guaranteed Ukraine's security in exchange for its denuclearization. The agreement promised that the United States, the United Kingdom, and Russia would not use force or threats against Ukraine, and would respect its sovereignty and borders.
By not protecting Ukraine we will look weak to Russia. And other countries will not trust our agreements and instead be motivated to make their own nukes, since they see they can’t depend on us