A major liberal group has drawn up a multimillion dollar plan to make Joe Biden cooler online. And the initiative has the blessing of a top White House official. The organization, ProgressNow, is launching a $70 million project to help the president and down-ballot Democrats win the war for voters’ digital attention. The idea is to create, in their own words, an “echo chamber” on the left. At its heart, it is an effort to compete with one they say already operates on all cylinders on the right.