Winning the presidency ultimately boils down to patching together enough states to win 270 or more electoral votes. According to an analysis by Politico, that task is almost entirely out of reach for Donald Trump at this point:
In June, POLITICO identified 11 key battleground states — totaling 146 electoral votes — that would effectively decide the presidential election in November. A new examination of polling data and strategic campaign ad buys indicates that six of those 11 are now comfortably in Hillary Clinton’s column.
Clinton leads Donald Trump by 5 points or greater in POLITICO’s Battleground States polling average in Colorado, Michigan, New Hampshire, Pennsylvania, Virginia and Wisconsin. If the Democratic nominee won those six states, plus all the other reliably Democratic states President Barack Obama captured in both 2008 and 2012, she would eclipse the 270-electoral-vote threshold and win the presidency.
Even if Trump ran the table in the remaining battleground states — Florida, Iowa, Nevada, North Carolina and Ohio — he would fall short of the White House if he cannot flip another state where Clinton currently leads in the polls.
It's probably too early to write Trump off once and for all, especially in a year in which the Cubs are still alive in their World Series chase. But without some significant external event that dramatically re-casts the election, it's almost impossible to see Trump closing the gap and winning on election day.