The red line has shifted but if the U.S. crosses it Putin has the will and the military capacity to punish the U.S. for promises that were made and broken regarding NATO in the 1990s. From Ted Snider at responsiblestatecraft.org:
Since its assurances not to move “one inch” outside Germany, the alliance as moved 600 miles closer to Russia.
It is possible to actually measure Washington’s dishonesty. How big is it? It’s about 600 miles.
In 1990, according to declassified documents, Secretary of State James Baker assured Soviet leader Mikhail Gorbachev that NATO would not expand “one inch” east of Germany. Thirty years ago, that was Russia’s red line.
On December 2, that red line moved from one inch to 600 miles as Vladimir Putin said he would now seek a promise that NATO would not expand further east to Ukraine.
Since these assurances, NATO has wandered its way through Hungary, the Czech Republic, Estonia, Latvia, Lithuania, Bulgaria, Romania, Slovakia, Slovenia, Albania, Croatia, Montenegro and Poland. Six hundred miles of broken pledges have brought the U.S. and NATO to the border of Ukraine.
On September 1, President Biden met with Ukrainian President Volodymyr Zelensky at the White House. Biden used code words for NATO encroachment when he pledged his “support for Ukraine’s Euro-Atlantic aspirations” and American support for Ukraine’s “being completely integrated in Europe.” He then announced “a new $60 million security assistance package” in addition to the $400 million in security assistance the U.S. has already provided Ukraine this year.
Having retreated 600 miles from Gorbachev’s red line, Putin drew a new red line on December 2, seeking “reliable and long-term security guarantees.” Those guarantees “would exclude any further NATO moves eastward and the deployment of weapons systems that threaten us in close vicinity to Russian territory.”
Putin is keenly aware that the red line has moved east 600 miles. At the Munich Conference on Security Policy in 2007, Putin asked the world, “And what happened to the assurances our Western partners made after the dissolution of the Warsaw Pact? Where are those declarations today? No one even remembers them. But I will allow myself to remind this audience what was said. I would like to quote the speech of NATO General Secretary Mr. Woerner in Brussels on 17 May 1990. He said at the time that: ‘the fact that we are ready not to place a NATO army outside of German territory gives the Soviet Union a firm security guarantee.’ Where are these guarantees?”