>> reporter: into dusk, the dig inches carefully forwards with no time limit or guarantee it will find anything. the city center swamped in dust and the heavy knowledge that the longer their patience and struggle, the less like i it is to be rewarded. nick paton walsh, cnn. u.s. president joe biden heads to poland later this month with the war in ukraine about to enter a second year. he'll arrive in poland february 20th, four days before the anniversary of russia's invasion. mr. biden will meet with his polish counterpart and other leaders from the region. the white house says he wants to send a message that allies will continue to stand by ukraine against russia's aggression. sam kiley has more now from eastern ukraine, where russian forces already are ramping up their attacks. >> reporter: clearly there's a great deal of interest in the visit of a u.s. president to poland to mark the anniversary