I picked "Using the IRS as a political weapon"....because it is closest to Subverting the Government...which he certainly has done.
The IRS could never have gotten away with what it did....if the Attorney General was doing his/her job, but neither who served did their job....because both were in the Hip Pocket of Barack Obama.
He corrupted every branch of a huge bureaucracy...he could do it because he corrupted the Justice Department...and that gave every Criminal in the Federal Government license to steal and cheat and oppress...See for example Secretary of State Hillary Clinton.
And that kind of power put him just a breathe and a blessed term limit away from a Dictatorship.
He is a Liar...a closet Muslim, a pretty much Out-of-the-Closet Socialist....and lastly, a Violator of his Oath to the American people; for he swore to faithfully execute the laws...and instead, in the case of Immigration...he affirmatively undertook to undermine those very laws....in the crass service of his political party.
He is a pompous arrogant ass, yet as complete a Fool as Jimmy Carter, i.e. Incompetent...which he mostly wiggles out of with his one of his two Great Assets---the ability to tell lie after lie adroitly.
Worst President in History....Would have been impeached if the ***** Republicans in Congress weren't scared shit-less of his Get-Out-of Jail Free RACE Card....his second Great Asset.