By David Shepardson Reuters (Adds more from Rubio, Commerce not responding to request for comment, background) WASHINGTON, Aug 17 (Reuters) - Republican Senator Marco Rubio urged President Joe Biden on Tuesday to block short-form video app TikTok in the United States after China took an ownership stake in a key subsidiary of ByteDance, the Beijing-based parent company of TikTok. The Biden administration in June withdrew a series of Trump-era executive orders that sought to ban new downloads of WeChat and TikTok. "Beijing’s aggressiveness makes clear that the regime sees TikTok as an extension of the party-state, and the U.S. needs...