At Real Clear Politics, I observe that Donald Trump has been under a ceiling of 45 percent in the RCP poll average for the entirety of the presidential campaign, while Hillary Clinton has largely been above it. There is some precedent for a candidate to break 45 percent for the first time late in the race, but only when something changes. Unless Trump changes, he's stuck. And it may well be too late.
The point in raising this is not to predict Trump's defeat (maybe Trump does change!) but to note that the basis of the Trump campaign to date — scapegoating immigrants and tarring Muslims — is a monumental failure.
America has simply become too diverse for a Nixonian "Southern Strategy" to succeed. No longer can a multicultural Democratic coalition be broken by race-baiting whites. Decades ago, as political scientist Michael Tesler has explained, white attitudes on race were more monolithic and susceptible to wedge politics. Today, such tactics are ineffective to dislodge white Democrats from their party.
The Trump campaign has been a test to see if the Republican Party can still win as an essentially all-white party with a platform rooted in racial grievance. All the evidence says it cannot. The Trump campaign can change now or the Republican Party can change later. There is no other option.