Czars:
What he's done is unconstitutional. Under the Article II Appointments Clause, such powerful officials must be confirmed by the U.S. Senate.
Executive Orders and Agency Actions:
What he's done is unconstitutional. Article I of the Constitution provides that only Congress can make laws, and administrative actions that are so broad they change public polity are instead considered lawmaking.
International Law:
The Constitution gives the President a lot of power when it comes to foreign policy. The President cannot do through treaty or foreign law anything the Constitution does not allow to be done through legislation.
(Which begs the question of whether our current activist Justices and Federal Judges should be removed from the SCOTUS and/or the Federal Courts for making rulings based on international or foreign law rather than the US Constitution.)
Health Care:
Parts of this are unconstitutional - i.e., mandated individual purchase of insurance and state-based insurance exchanges. The whole damned thing needs to be repealed.
Card Check:
There's a question of whether this is Constitutional - depends in part on how it's implemented.
Census:
What is being done with statistical sampling to reallocate congressional seats, redraw legislative districts, shift Electoral College votes is not Constitutional. The Census requires an actual count of persons, and may require the counting of citizens, not just persons.
DC Voting Rights Bill:
Not Constitutional. The District of Columbia was created to be, is, and always has been, a Federal jurisdiction and our elected Representatives and Senators represent only those Americans who live in states.
Solution: If you want to vote, move to Maryland or Virginia.
Guns:
Most anti-gun actions violate the Second Amendments rights to keep and bear arms.
Education and Religion:
The whole secular society thing where government controls all education and interferes with religion is unconstitutional. Parents have a right to raise their children as they see fit. So basically all the efforts by the Far Left and "Progressives" to rid the US of religion (and by default, education) is in violation of the Constitution.
Please purchase or borrow from your public library The Blueprint: Obama's Plan to Subvert the Constitution and Build an Imperial Presidency by Ken Blackwell and Ken Klukowski if you're interested in reading the arguments/explanations. It's a very interesting read.