John Bolton: Our biggest mistake in the 1990s and during the Bush administration was leaving Ukraine, Moldova, and Belarus in a gray zone - not pushing harder for their eventual NATO membership. Eastern and Central Europeans were begging for protection from Russia. We expanded NATO but left a dangerous gap that Russia quickly exploited. In 2008, Bush tried to fast-track Ukraine and Georgia into NATO, but France and Germany blocked it. Ukraine is an incredibly rich and powerful country that is striving to become truly European and Western - while rejecting Vladimir Putin’s aggressive nationalism.