evidence of that. in fact, president biden saying 150,000 russian troops are now on ukraine's doorstep. invasion he says remains distinctly possible. in some of the clearest terms yet, mr. biden laying out what is at stake, the human cost to ukraine, the strategic cost to russia, and a potential jolt to the american economy from disrupted energy supplies. we're covering it all from washington to ukraine where we start with richard engel. >> reporter: tonight president biden's bleak warning about the looming russian threat on the ukrainian border. >> an invasion remains distinctly possible. >> reporter: he laid out two paths, promising punishing sanctions if president vladimir putin invades, while saying the door to diplomacy is still open. >> we should give the diplomacy every chance to succeed. and i believe there are real ways to address our respective security concerns. >> reporter: it comes after a day of mixed