That was candidate Trump speaking in 2016. I think he really meant alone, meaning “by himself.” He apparently forgot, or at least misunderstood, that we live in a democracy. The presidency is only one branch of our government. There is a Congress composed of 100 Senators and 435 members of the House of Representatives, most of whom came to Washington with the expectation of playing a part in governing the country, and a Judiciary, judges who protect the Constitutional rights of all people.
Trump fancies himself the ultimate dealmaker, so he probably believed he alone could fix “it.” To paraphrase Bill Clinton, it depends upon the meaning of the word “it.” During his campaign, on October 22, 2016, Trump issued what he called his Contract with the American Voter. It was a plan that would guide his administration starting from the first day, and contained 60 promises. These are Trump’s top ten promises: Number one, of course, was to build a wall along the southern border, and number two, he would make Mexico pay for it.