Sarah Longwell, a one-time Republican pollster who has kept her distance from the party ever since the emergence of former President Donald Trump, said the GOP made a grievous error by setting expectations so low for President Joe Biden’s State of the Union response. Appearing on CNN Friday morning, Longwell said that Biden delivered an excellent address by any standard, but she added that its impact was enhanced because Republicans had spent so months writing off Biden as a doddering invalid on the cusp of death’s door. “Last night, what he said was for the Democratic base,” Longwell explaine…