Because a number of Republicans have actually suggested that Obama should be impeached for daring to use executive orders to enact gun control measures...
"Republicans Accuse Obama of Using Position as President to Lead Country" by Andy Borowitz
"Spearheading the offensive was Rep. Steve Stockman (R-Texas), who charged the President with the “wanton exploitation of powers that are legally granted to him under the U.S. Constitution.”
Calling him the “Law Professor-in-Chief,” Rep. Stockman accused Mr. Obama of “manipulating a little-known section of the Constitution,” Article II, which outlines the power of the President."