The U.S. escalation in Ukraine actually has a plan. This is just a small semantic manipulation, which is contained already in the title of the RAND commentary. The plan is to force Russia to make peace.
Being in Moscow at the moment, I can tell that this plan is taken absolutely seriously by the Kremlin and it is causing some mild alarm here. After the leading NATO powers authorized Ukraine to strike Russian territory with their weapons, we are not talking about "escalation in Ukraine," but escalation in Russia. Many observers here are seriously drawing parallels with Yugoslavia in 1999 when NATO strikes on Belgrade were used to force Milosevic to withdraw from Kosovo. For Russian elites, such parallels are humiliating because the Russian Federation is a nuclear power, with the world's second largest nuclear arsenal.
At the same time, everyone realizes that nuclear blackmail does not work, primarily because there are no real "red lines," as you absolutely rightly mentioned. In this case, there is a dilemma for the Kremlin: raise the stakes with the prospect of approaching the need for real fulfillment of the nuclear threat, or look for pragmatic ways for possible exit strategies. These strategies will not necessarily look like de-escalation on the front, which is what we are actually seeing in Kharkiv. It seems that the Kremlin is currently choosing the second option.