It's very strange that losing a Presidential general election is seen as the end of a political career when in years past, candidates like Bryan, Stevenson, or Dewey were still seen as viable.
Also, your explanation of Dewey choosing a political stance that was widely held among voters but somewhat taboo among the political class and riding that stance to prominence shows that there's really nothing new or innovative in the wave of populism sweeping Western democracies in recent years.
It's true, but it's worth noting that while in modern times losing is generally a career-ender for candidates it is much less so for the operatives behind the scenes, some of whom spend their whole careers cycling from one losing campaign to another. The most striking example of this is Democratic consultant Bob Shrum, who was behind the curtain for a remarkable eight losing presidential campaigns. (See http://www.washingtonpost.com/wp-dyn/articles/A9895-2004Sep9... for a good profile of Shrum, written as he was on his way to his eighth defeat in 2004.)
To be fair, though, between the years of 1972 and 2004, the only two winning Democratic candidates were Jimmy Carter and Bill Clinton.
You could tell a similar story for any Democratic strategist with an overlapping career. Tad Devine worked for the failed campaigns of Mondale 84, Dukakis 88, Kerrey 92, Gore 00, Kerry 04, and Sanders 16. (He also worked in Ukraine on Viktor Yanukovych's winning 2010 Presidential campaign, alongside Paul Manafort. Small world.)
Also, if you work for a successful Presidential election campaign, you end up working in the White House, e.g. George Stephenapolous, Karl Rove, David Plouffe, David Axelrod, and Steve Bannon.
Candidates like Clinton falter because they suck. Kicking off your campaign Roosevelt Island and driving to Pennsylvania or wherever in a hotel shuttle van was the kickoff to a weak campaign.
Bimetallism can never work, because the amount of silver relative to gold is never fixed. It has all the fundamental faults of "pegging" one currency to another.
How do you propose I judge which of you is right?
A great short biographical sketch can be found in Richard Hofstadter's classic The American Political Tradition and the Men Who Made It (https://www.goodreads.com/book/show/773961.The_American_Poli...), which is an excellent, compulsively readable book, though Hofstadter had a low opinion of Bryan so this is not the source to turn to if you want to argue with me. The "I will look up the arguments later" quote can be found in Robert Cherney's A Righteous Cause: The Life of William Jennings Bryan (https://www.goodreads.com/book/show/1704339.A_Righteous_Caus...), which I haven't read myself but looks to be a good general-interest book-length biography. A contrarian view on Bryan can be found in Michael Kazin's A Godly Hero: The Life of William Jennings Bryan (https://www.goodreads.com/book/show/79196.A_Godly_Hero), but the rehabilitation of populism has been a project of Kazin's for decades now, so it will come as no surprise that Kazin has more respect for Bryan than most historians.
This gets the causality backwards. What Bryan decided was that he wanted to be President, and that in order to become President he would need to associate himself with an issue hot and controversial enough to attract voters to him for having taken their side on it. Bimetallism was a live-wire issue among the rural constituency he wanted to set himself up as the champion of, and it had few other champions due to the oppressive orthodoxy the gold standard held over the thinking of the time, so he chose that as the issue to wrap his arms around.
It worked -- Bryan stood out to rural voters as the one politician who really understood their needs, and his career as "The Great Commoner" was born. But Bryan's adoption of bimetallism came because he recognized its political potency, not because he held strong opinions about the economics of the matter. He cared so little about those that, when questioned about the details by an Omaha newspaper, he replied that "I don't know anything about free silver. The people of Nebraska are for free silver and I am for free silver. I will look up the arguments later."