President Biden today said he believes Putin has made the decision to invade and will start an invasion in the coming days.
He and his administration probably does in fact believe that, but I still lean toward thinking that they're being played. I don't think that Russia will do anything that will result in most NATO countries saying, "Yep, that was definitely an invasion of Ukraine, so now we're doing all of the crushing sanctions we'd planned." If Russia fully withdraws without much incident like they've been publicly saying, then at this point it'd be a big blow to the credibility of Biden/America/NATO. Even more likely is that they continue their threatening posture to keep the West in an uncomfortable state of limbo for months.
It is hard to say what is actually known, and how reliable the intelligence is.
When we withdrew from Afghanistan, the US intelligence predicted that it would take months for the Taliban to take over the country when it actually took about 48 hours, and there was nearly zero resistance. Now US intelligence is saying that Ukraine could fall within 48 hours of Russia launching an invasion. I am not sure the basis for that prediction, however, I do believe there will be much more resistance to an invasion as Ukraine has resisted Russia in recent years.
It does appear that western intelligence was right about a false flag operation. There was a bombing against the leader of a separatist group that had no casualties. I would expect a failed assassination attempt to have
some civilian and/or security casualties.
I wouldn't bet much against an invasion, though, and on the other side of the argument, if Putin knows that he eventually wants to take a piece of Ukraine, now would be the perfect time. The energy market is currently uniquely favorable to Russia, German politics biases them strongly against cutting all ties with Russia, Putin needs a boost in his domestic approval, etc. Also, if Trump is president in 3 years (a distinct possibility), then an attack against Ukraine years in the past under Biden isn't something that Trump would particularly care about.
It looks like if they will do something, we're most likely to see it in the next few days.
Putin has claimed to be withdrawing his troops from the Ukraine border, but there does not appear to be evidence of that. It does appear that war is imminent.
The best time for Russia to invade would be after the Nordstream 2 pipeline is complete (perhaps one year later), during the winter, when Europe would be dependent on Russian gas via the pipeline. Germany and Frace appear to be the weak links in potential sanctions against Russia. That is fitting considering that an invasion of Ukraine would be the biggest war in Europe since WW2, and neither country was on the right side of either world war (Germany was part of the Axis, and France quickly fell).
Trump is not going to start a new war in response to a Russian invasion, although I do believe he would be open to continuing military operations in the region if he is convinced that is what is best for the US. Trump was harder on Russia than either Obama or Biden, despite the baseless claims of being a Russian agent.
The Ukraine president has called for a meeting with Putin, so the two sides can come to a peaceful "settlement". It is possible that Ukraine will be willing to give up some of its territory in exchange for the promise of peace. This could be seen as a win at home for Putin (which is likely the root cause for the Russian aggression), and would avoid the bloodshed associated with war.