The "power" he is granted by the Constitution and the "power" he uses are two different things.
Look for FBI background checks to be put "on hold" or some such. Then they can start denying FBI checks for parking tickets and overdue library books. If they can reduce the number of "legitimate" sales to a low enough point many gun dealers will go out of business.
"In every generation, there are those who want to rule well - but they mean to rule. They promise to be good masters - but they mean to be masters." - Daniel Webster