"Since compensation is set by statute, Trump can't actually refuse to take it - just like George Washington, who reportedly tried to refuse a salary but got paid anyway, at $25,000 per year.
That said, Trump could opt to donate his salary to charity or return it to the Treasury: he wouldn't be the first President to do so. When John F. Kennedy was President, he donated his salary to charity..."*
And I'd bet that they deducted the contribution from their taxes.
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*http://www.forbes.com/sites/kellyphillipserb/2016/11/14/trump-says-no-to-presidential-salary-could-you-do-the-same-cut-your-tax-bill/#25b7ea3e3401