(CNN) — Joe Biden's presidential campaign is now asking Twitter to reject a video ad from President Donald Trump's reelection campaign that falsely accuses the former vice president of corruption for his role in Ukraine policy during the Obama administration. In the letter, first obtained by CNN, the Biden campaign asks Twitter to reject the ad should the campaign place it again. While the letter, written by Biden campaign manager Greg Schultz, acknowledges that the social media company has said the ad complies with its policies, he asks that Twitter "promptly reassess" that position. Specifically, the letter calls on Twitter...