For months, this election was all about angry voters demanding change. They seemed to echo the plaintive cry of Howard Beale in the movie “Network,” who screams to the world, "I'm as mad as hell, and I'm not going to take this anymore!"

The Republican strategy--and that of Bernie Sanders--was to build on this popular resentment, pin the label of "status quo insider" on Hillary Clinton, and hope to build a winning coalition.

That strategy worked in the primaries. Among Republicans, it killed off establishment candidates, from Jeb Bush to Marco Rubio, leaving a two-man fight between outsiders Donald Trump and Ted Cruz. It almost worked among Democrats, where Clinton had to sprint to beat a grumpy socialist with no legislative achievements and no national stature before the primaries.

Now, in the early stages of the general election, that strategy is faltering. Why? Not because voters are suddenly happy with the status quo. They are still disgusted with established politicians, insider deals, slow economic growth, and rising dangers at home and abroad. They still don’t trust Washington insiders to solve those problems. They still think those insiders are cutting special deals for themselves and cutting out ordinary people.

But those anxieties are now being eclipsed by another, even larger one. Voters are increasingly worried Donald Trump is not stable enough to be entrusted with the vast powers of the presidency, not prudent enough to make life-and-death decisions, and not respectful enough of constitutional limitations to head the executive branch.

Trump is in deep trouble, not because he's an outsider, not because of his controversial views on trade and immigration, but because the American public increasingly sees him as erratic and undisciplined. They see his attacks on John McCain, Megyn Kelly, and others as worse than "mistakes." Voters are beginning to think they reveal deep-seated character flaws—flaws that he would inevitably bring to the Oval Office. For Trump, that perception is disastrous.

Hillary Clinton is certainly painting him that way. She's getting a lot of help from a friendly media (who are less pro-Clinton than anti-Trump), and, most of all, from Trump's own impromptu remarks on the campaign trail. In her narrative, Trump is beginning to resemble the Glenn Close character in “Fatal Attraction,” whose weekend fling with a married man (played by Michael Douglas) turns into his nightmare as it dawns on him that, however enticing she was at first glance, she’s really irrational, obsessive, and dangerous.

Once voters believe that about Trump, their views are likely to stick. Like red wine spilled on a white carpet, you can scrub and scrub, but you cannot erase the stain. To be considered erratic and impulsive, driven by pique and personal grudges, is just such a stain. Voters know, in their guts, that all presidents must make momentous decisions under great stress and great uncertainty. They want stability, careful consideration of alternatives, and calm, prudent judgment.

Neither candidate receives high marks for good judgment. Republicans initially thought they could use the issue to attack Clinton. She’s vulnerable on multiple fronts. She pushed hard to remove Libya's dictator, Moammar Gadhafi, and reaped the whirlwind. Her much-touted effort to “reset” U.S.-Russian relations failed utterly. She is closely tied to the Obama administration’s bumbling Middle East policies, which led to deepening civil wars, coups and counter-coups, and widening influence for Iran and Russia. She is indelibly associated with the ensuing global dangers.

That dismal record would sink most candidates, but not with Trump in the race.

He is even more vulnerable because his judgment looks even worse: He’s impulsive, narcissistic, and dangerous. If he cannot reverse that perception before it hardens among voters, then he is doomed. And that perception is hardening quickly.

Trump's sinking popularity does not ensure Clinton's victory, but it does sharply increase the odds. The PredictIt betting market now puts her odds of winning at 75 percent. What could save Trump? Perhaps a WikiLeaks email dump that contains a smoking gun. Perhaps a major corruption scandal involving the Clinton Foundation. Perhaps a major terrorist strike in the U.S., especially one that could be linked to failed U.S. policies.

For now, though, Trump is painting himself into a corner, and Clinton's negative ads in are keeping the paint wet. The electoral map is widening, to her benefit. States once considered reliably Republican are now suddenly in play. Down-ballot Republicans are distancing themselves from the presidential ticket, partly because Trump is trailing, partly because they fear what he might say next. Their fears are well grounded.

Independent voters are beginning to shift. Polls are still fluid because the general election is only beginning and because pollsters cannot determine “likely voters” until September. But if voters decide Trump is unstable, unpredictable, and unreliable, they will make him unelectable.