WASHINGTON - After three nights of solemn political rhetoric at the U.S. Democratic National Convention, comedian Julia Louis-Dreyfus injected a heavy dose of humor and mockery on Thursday, all of it aimed at Republican President Donald Trump. Louis-Dreyfus, best known as the fictional vice president on the HBO comedy “Veep,” moderated the final night, firing off a string of one-liners and lightening the earnest tone of the convention to nominate Democrat Joe Biden for the White House. When the actress described herself as a union member, climate activist and patriotic Democrat, she added, “or as Donald Trump will call me in a tweet tomorrow, a washed-up, horse-faced, no-talent, has-been with low ratings,” she said. “Well, with all due respect, sir, it takes one to know one.” After a video addressing Biden’s faith, she made reference to Trump’s famous walk across Washington’s Lafayette Square in June for a photo-op in front of a church, aided by officers forcefully clearing the way fo