Once again, EOs can only be used to enforce existing law ...
No, once again, that is not quite correct. Executive orders in and of themselves have the full force of law, as they are either made in pursuance of some Act of Congress (and that gets stretched a bit, sometimes), or an authority granted to the Executive that was granted under the Constitution. A Congressional override would require a supermajority, which might be tough to obtain.
However an Executive Order can be challenged in court, if someone feels it exceeds Presidential authority. However, of course, the plaintiff would face the combined weight of the White House and Justice Department legal staff, so that would be quite a battle.
An executive order that overreaches and infringes on 2A could readily end up in the Supreme Court, and no administration would relish a thumping by the Supremes on a high profile issue if the SC agrees that the EO went too far.
However, if Congress is not seen as doing something, I can very well see this White House coming in through the back door with some Executive Orders that would fall directly within their domain (ideas I have heard put on the table include a renewed ban on the import of certain weapons, parts and magazines, a ban on the import of certain kinds of ammunition, and moving "assault weapons" to an NFA category.)
