WASHINGTON — During his campaign, Donald Trump often bragged about his skill as a negotiator.

In conversations, he ventured that, as president, he might be able to resolve two of the most thorny and tragic dilemmas: finding peace in the Mideast and reaching a sensible compromise on guns.

He said he would hop in his limo and go to N.R.A. headquarters in suburban Virginia and stay as long as it took to make a deal, noting that there were points where both sides in the debate could agree.

Even if Trump once had some negotiating aptitude — his biographers say it was rare — we have seen his art-of-the-deal aspirations evaporate in a cloud of self-absorption, as one tableau of legislative chaos after another unfolds.

Trump wrote in his 2000 book, “The America We Deserve,” that he was in favor of a ban on assault weapons and “a slightly longer waiting period to purchase a gun.” But then the N.R.A. spent more than $30 million to get him elected. All his earlier moderate positions withered as he slavishly followed the money and applause from the basest of his base.