The head of the GOP can spend all the time he wants on the campaign trail, paid for by the GOP. Same for the rats.
POTUS, or a US Senator/etc, has a different job to do, paid for by the taxpayers' grandchildren.
So, politicians should never interact with their constituents? And, there really isn't a whole lot of localized security expenses when Trump's C-32 pulls up to a small town hanger like in Mosinee last night or Elko, NV last weekend or any of the small cities he's been visiting..
Check the places he's rallying. He's not shutting down major metropolitan areas where streets need to be secured and blocked etc. His rally in Charlotte is going to cause some disruptions - and certainly his visit to Houston required local support - but I've recently seen him in Mosinee, WI, Elko, Missoula, Evansville, Erie, Wheeling, Southhaven (Miss), Topeka, Springfield (MO), Richmond (Ky), Johnson City (TN), Rochester (MN), Council Bluffs (IA), Fargo, Lebanon (OH) etc. etc.