It's Trump's safest ground. Polls consistently show the Republican nominee with an advantage on the economy, though Democrat Hillary Clinton has been cutting into that lead in recent months and plans a rebuttal speech of sorts on Thursday in Detroit.

The main element of the latest effort at campaign normalcy comes Monday in an economics speech in Detroit in which Trump will lay out a plan for tax cuts, infrastructure spending and revamped trade deals he claims will double the pace of economic growth.

Trailing badly in national and swing-state polls, Trump has no choice but to try, but there's no reason to believe it will work.

As the 2016 campaign heads toward a late-summer lull, Donald Trump is trying for yet another reboot.

Republican presidential candidate Donald Trump takes a paper out of his jacket during his rally at Windham High School on August 6, 2016 in Windham, New Hampshire.

Trump's speech comes after weeks of bleeding in which he picked an enormously damaging fight with the parents of a Muslim-American solider who died in Iraq, feuded with party leaders including House Speaker Paul Ryan and Sen. John McCain, R-Ariz., repeatedly threatened to ditch long-standing American alliances and called on the Russians to help him by leaking more damaging information on Clinton. That's only a partial list of Trump's headaches since the GOP convention, which according to Gallup was the first ever to leave voters less inclined to vote for a party nominee.

The damage is obvious. Trump now trails Clinton by an average of 7 points. States that should be competitive for Trump, including Virginia and Colorado, now appear safe for the Democratic nominee. Trump is increasingly reliant on a low-probability Rust Belt strategy that would require him to win Pennsylvania, where he now trails by an average of 7 points.

And on Monday, Evan McMullin, a former CIA agent and Goldman Sachs executive who ran policy for House Republicans, announced he would seek the presidency as an independent, another blow to Trump's chances. McMullin will give "Never Trump" Republicans uncomfortable with libertarian candidate Gary Johnson a place to go, and potentially put deeply red states including Utah, where Mormons despise the GOP nominee, in play for Clinton.

So a reboot is desperately needed. The effort began with Trump's reluctant endorsement of Ryan, McCain and New Hampshire Senator Kelly Ayotte in their primary campaigns. And Trump became somewhat less voluble on Twitter over the last few days.

But we've seen this movie before.

Trump allies promised a new, more traditional political approach in April. It never happened. They promised it again after Trump fired Corey Lewandowski as campaign manager in June, vesting all power in long-time GOP consultant Paul Manafort. Again, the "pivot" lasted just a few days before the free-wheeling, thin-skinned Trump, who can seemingly resist no provocation, was firmly back in control.

Because this is who Trump is. He is a 70-year-old hot head who cannot stand for the conversation to be about anything other than Donald Trump. That means any attempt to focus exclusively on making the race about the economy and Clinton will never succeed.

Trump was back at it on Twitter over the weekend, lashing out at Michael Morell, who wrote a highly critical op-ed about Trump. The candidate called Morell "the lightweight former acting director of C.I.A., and a man who has made serious bad calls … a total Clinton flunky!"

He let the media have it as well, and in the process offered up a litany of his own mistakes: "The media is going crazy. They totally distort so many things on purpose. Crimea, nuclear, 'the baby' and so much more. Very dishonest!"

Trump has shown himself able to surrender to his handlers for a few hours and read a prepared policy text off a teleprompter. Backers then declare that he has pivoted to a potentially successful strategy against a vulnerable Democratic nominee. Then it all comes crashing down. And it will again.

Trump will revert to lashing out, alienating all but his hardcore supporters and crying about a potentially "rigged" election outcome without any evidence to support such corrosive and dangerous claims. And then he will go on to lose, possibly in epic fashion, and Republicans will be left to pick up the pieces of a shattered party.

—Ben White is Politico's chief economic correspondent and a CNBC contributor. He also authors the daily tip sheet Politico Morning Money [politico.com/morningmoney]. Follow him on Twitter @morningmoneyben.

