US President Donald Trump's first campaign rally in months took place in Tulsa, Oklahoma, on June 20, 2020, but only hosted only a fraction of the number of supporters his staff expected. Some of the no-shows may have been teenagers who registered to attend the rally but stayed home. Days before the event, calls went out on social-media apps TikTok, Instagram and Twitter, asking Trump opponents who had no intention of going to the rally to sign up anyway. The message spread among teens,…