"Drain the swamp" was a late development in the campaign, courtesy of the libertarian Steve Bannon and former Cruz campaign manager Kellyanne Conway, also a libertarian. Arguably if Trump had dropped that rhetoric and pretended to make nice with the Establishment after he'd won we'd see far more of the things Trump ran on accomplished by now than we do.
Trump distinguished himself from every other candidate in the primaries by making the border with Mexico the central issue from the time he walked down that elevator until mid-August 2016, which, when solved, would help to solve many other problems, like drugs, disease, and crime. After Bannon and Conway came on board replacing Manafort, however, that message began to be played down, to the point that Trump's campaign nearly cratered in the Arizona town hall in late August with Sean Hannity when Trump wavered badly on the issue, polling the crowd for its opinion. That was not the same man we had been seeing for an entire year.
Rush Limbaugh is also a libertarian, and characteristically doesn't give a damn about the border. He never has. He just licked his finger and checked the wind in his support of border security under Trump. But illegal immigration was never on Rush's radar, just as it wasn't on Ted Cruz' either. Rush was for that dual citizen, remember?
Here is Rush today, still trying to co-opt the Trump base:
That’s why at every Trump rally, what is the No. 1 sign they see, outside of Make America Great? What’s the number one sign you see at a Trump rally, Mr. Snerdley? (interruption) Nope. “Drain the swamp.” “Drain the swamp” is the No. 1. “Build the wall,” No. 2. (“Lock her up” is really a chant.) But “drain the swamp” is why Trump was sent there, and declassifying these documents would be a giant step for mankind in draining the swamp.
Wikipedia gets some things right:
