Campaign tweet-fight! Clinton, Trump camps brawl on Twitter

Trump started it, mocking President Barack Obama's endorsement of the presumptive Democratic nominee on Thursday.

"If anyone knows how to use a delete key, it's you," replied Reince Priebus, chairman of the Republican National Committee, in a reference to the messages Clinton deleted from the private server she used for her correspondence at the State Department.

Weiner resigned his seat in Congress after sexual messages he sent over the social media site became public.

When Clinton announced in March 2015 that she had turned over 55,000 pages of emails to the State Department for public release, she also she said she "chose not to keep my private, personal emails."