Assuming he donates all of his salary (as the Consitution requires that the President be compensated, at least $1 as past presidents, like Kennedy have done) something he has rarely followed through in the past (Throughout his career, he has promised to donate about $45 million of his own money, the actual amount, while generous, is $7.8 million) technically he will cost the federal government more than his salary…So instead of taking $1, he is pledging to donate his salary, altruistic as it is, it will cost the US Treasury more than it would have then if he had just taken $1 (or the $400k to take his salary…Let me explain.
Ok, so, under his current plan to donate his salary, Trump will not only be taking the $400,000 salary, but he will also be given a tax break on the donation (again assuming he takes then donates it all)—money that would have been taxed with a portion to have gone to the U.S. Treasury. Depending on Trump’s income bracket, he will be given a tax break between $140,000 and $156,000 on the $400,000 donation. In the end, Trump’s salary will cost the Treasury between $540,000 and $556,000, making Trump the highest-costing president in U.S. History.
A minor point and not one that I personally don’t care about, but I can’t help by note the irony as Trump supporters, by and large, believe that this is a measure to lower federal spending when in fact it will cost the Treasury more.
[EDIT] After giving it some thought, some of the donations may be considered income, so it’s possible that the number could be a little lower, but donation to the park service (as an example) wasn’t taxed and many organizations aren’t taxed for “gifts”, but it depends on where the money goes, if we’re being technical.