Iran nuclear deal
The deal limited Iran's uranium enrichment, but it did not stop Iran to support terrorist groups like the Muslim Brotherhood, Hamas and Hezbollah. It also did not address Iran's expansionist ambitions in the Middle East. 
- See also: Mueller office
The report of Special Counsel of Robert Mueller flatly states that Russia began interfering in American democracy in 2014. Over the next couple of years, the effort blossomed into an attempt to interfere in the 2016 presidential election. The Obama administration knew this and did nothing. National Security Advisor Susan Rice told her staff to "stand down" and "knock it off" against the Russians. Obama was singularly focused on the nuclear deal with Iran. Obama wanted Vladimir Putin in the deal, and to stand up to him on election interference would have, in Obama's estimation, upset that negotiation.
- (Ghoraba, Hany). Why Egypt Supports U.S. Withdrawal From Iran Nuclear Deal. The Investigative Project On Terrorism. Retrieved September 2, 2018.
- (Keinon, Herb). NETANYAHU APPLAUDS TRUMP’S ‘BRAVE DECISION’ TO PULL OUT OF IRAN DEAL. Jerusalem Post. Retrieved September 2, 2018.