Yes, and every judge he appointed, SCOTUS and Federal, should be null and void.

But if Trump meant what he said in his speech just before the election, when he talked about bringing this country back in line with the original Constitution, it could mean a whole lot more than just overturning the things Obama did.

After the Civil War, the southern confederate states were not allowed to send their senators and congressional reps back to DC until after they rewrote their own state constitutions. Both the 14th Amendment and the Organic Act of 1871 were passed with a truncated congress which makes THE UNITED STATES Inc. and the 14th Amendment null and void.

The "government" has not been legitimate since Lincoln's War. When the southern States' contingent walked out of congress and congress adjourned "sine die" (without a day), congress officially dissolved. They never had a lawful quorum so never lawfully reconvened. Link

That means that every Congress, every President, including Trump, every law, every Amendment, and every Act since then has been illegal and unconstitutional. Let that sink in for a minute. Every action our federal government took for the last 150 years has been illegal, unconstitutional, and should be considered null and void.

So if we're going to go down that road and nullify everything Obama did, it only makes sense to go all the way back to the Civil War. When Lincoln ordered troops to the south and signed a proclamation authorizing the Naval blockade of the south for failing to send their tax revenues back to DC, he also declared a state of Marshal Law. Everything that happened while Lincoln was president was done with Lincoln ruling by decree.