Republicans are quick to suggest that President Joe Biden has lost a step — but he proved nimble enough Tuesday night to box them in on Social Security and Medicare. And he did it, in part, by going off script. Nearly halfway through his State of the Union address, Biden said that "some Republicans want Medicare and Social Security to sunset every five years" and that others would like to use the possibility of defaulting on federal debt as leverage to cut those programs. Republicans jeered. Rep. Marjorie Taylor Greene, R-Ga., a newly empowered voice in her party, yelled, "Liar!"...