Donald Trump is far ahead in the Republican polls but Democrats still believe that his emergence is good for them because it will undermine some other person who will become the Republican nominee. I am not sure that they are right.
In addition to his poll numbers, Trump has two major advantages on the path to the White House. First of all, he is from outside of politics. As an outsider, he can tap into the enormous frustration the American people have with politicians, gridlock, the administrative complexity of government, the corruption of the system by lobbyists, and the general feeling that the whole process is being run to serve "someone else." In the Republican primaries and then in the general election, his most likely opponents will be Senators and former Senators (Cruz, Rubio, and Clinton) whose voting records can be mined for information vital to attack ads. Trump has no voting record. He - like most of us - can claim to be an outsider. The two most successful Republicans since World War 2, Eisenhower and Reagan, like Trump, spent most of their lives in occupations other than politics.
The second advantage is much more important. Trump has a high level of experience and performance on television. The efficacy of both Presidential candidates and actual Presidents depends heavily on television performance. Deep down, the American people are asking themselves about each of the candidates - "Do I really want to see this person on my TV screen for the next 4 or even 8 years?"
Trump has been winning the "air war" and his facial expressions recall Reagan's ability to "shrug" at opportune moments. Trump is, of course, experienced as a TV personality from the successful show, The Apprentice. Regardless of one's views on his policy positions, the one thing you can't accuse Trump of being is boring. I saw this with Ronald Reagan midway through the Carter Administration and I picked him early to win the 1980 election for this reason. And - let's face it - some of the other candidates might get tedious as we viewed them for hundreds of hours on television. I think that this was one of Gore's serious problems in the 2000 election.
Of course, Trump has come out with some zany policy proposals. But - for all of his life - Trump has been a master of the Etch-A-Sketch. He can invest heavily in an area, persuade lenders it is a gold mine and then bail out with a well executed Chapter 11. If nominated, he would likely move to the center and "explain" some of his ideas in more practicable terms. He would be attacked for flip flopping but - running against Clinton - he would be able to go on the offense on the flip flop issue as well. His supporters would likely stick with him as long as he did not advocate an overtly socialist agenda.
I am not saying he will win but it is - increasingly - something that cannot be ruled out. Many of the things being said about him were said about Reagan at various points leading up to the 1980 election.
My "dark horse" candidate is premised on a long, drawn out Republican primary season with no clear winner. I believe that there is a non-trivial possibility that a deadlocked Republican convention will nominate Paul Ryan as its Presidential candidate and, if nominated, that he would have at least an even chance to be elected.
Disclosure: I/we have no positions in any stocks mentioned, and no plans to initiate any positions within the next 72 hours.