I believe that Donald Trump is a completely viable candidate. He has made his mark on conservative politics despite not being a conservative, he is a polar capitalist with moderate views on a lot of other issues. He lays on heavy with the rhetoric that is being judged as "racist" even though Muslims are not a race and neither are Mexicans. I do not agree with a lot of his rhetoric but I have studied his platform as much as I can and I personally do not have much of a problem with a lot of it.
In regards to a Trump presidency, personally, the chances of that are fading fast but not because Trump is still being Trump. It is fading for two reasons. One, the predicted spread of the Electoral College here in the United States was already stacked against ANY republican candidate. Even with Ben Carson or Jeb Bush, a lot of Republicans ideal cadidates (too bad they just couldn't take the heat) it would have been very tough for a Republican to win the election in 2016. And two, there currently is a surge of strong third party support. With both Trump and Clinton's approvals in the upper 30's or low 40's depending on what source you use, it shouldn't be a surprise that the Libertarians (Gov. Gary Johnson-Gov. Bill Weld) and the Greens (Stein) are making broad leaps in the polls. Between them they hold about 17% of the popular support.
Trump will definitely get the Republican nomination on the 18th. Hillary will get the Democratic. And with so much up in the air what with the 3rd party candidates, it is extremely unlikely that Trump will get the 270 Electors needed to secure the Presidency. EVEN IF HE DID, I think that Trump will be more malleable than either Congress or Trump himself cares to admit. DC doesn't like him but everyone seems to forget that the United States has a system of Checks and balances built into the government structure. Trump will not start WW3, if that starts anywhere it will be due to the NATO-Russian aggression in Eastern Europe or the US/Pacific Nations-China aggression in the South China Sea right now.
In the later, there isn't much Trump could do that Obama isn't already doing. Deploying more ships and effectively "flexing the American muscles" at China while still toying, manipulating, and otherwise intruding with the smaller nations contesting with China. The only thing Trump could add to the mix would be his "Stand Tall and Tough!" rhetoric which I don't think will either deter nor expedite China's inevitable military annexation of the entire region followed by the ousting of the US and other nations. And call me crazy but even though we shouldn't be over there in other people's business in the first place, If we keep up this destructive policy of drawing lines in the sand for Russia and China and then letting them cross those lines without consequence then we are just telling the nations of the world to stop taking us seriously. I don't agree with intervening but if we must then we have better not back down at the last minute and let Russia and China walk all over us. It is pathetic. And in that way I personally think Trump would handle the situation well because should he get in the White House China and Russia will learn quickly that our fast-talking and belligerent President doesn't want to play games.
I have my own prediction of how this election will turn out
that I posted here. But overall, although Trump's route to the White House is getting smaller and smaller, I don't think he would be the worst president we have ever had or could have and I do not think he will start WW3.