At this point trump seems oblivious to the investigation into obstruction or perhaps believe he is above any laws...
Don't know if I'd say "huge" (it would be huge, though, coming from any other President), but I think it's one of his more audacious tweets and deserves at least a censure from a responsible Congress. Very unethical to use his presidential powers to pressure an agency to make openly partisan decisions. It appears that Trump intends to fire Sessions after the midterms. That move can easily figure into any accusation from Mueller on obstruction of justice, and this tweet will be an exhibit.
Special guest appearance by mario rubio... and gee, if only mario knew a group of elected officials whose role was to create effective legislation and had powers to counter the reality TV contestant running the government...
LOL... though I bet he'd get the spelling of President Obama's middle name if he'd thought to include it.
Several places maintain a history of all his deleted tweets, like ProPublica - https://projects.propublica.org/politwoops/user/realDonaldTrump