The U.S. announces a withdrawal from a key nuclear arms control treaty with Russia. President Trump welcomes Chinese officials to the White House for two days of high-level trade talks, as the two countries continue to work on a new agreement. Further unrest in Venezuela over a fight for leadership rights. Plus -- much of the U.S. struggles with a deadly polar vortex. CBS News Correspondent Steve Dorsey will have these stories and more on the CBS News Weekend Roundup.