Republican strategists are understandably miffed that Donald Trump has degraded their brand with his bullying antics. But what they worry about more is the effects of Trump running as a write-in candidate.
If Trump loses the GOP nomination, runs as a write-in candidate after the primaries and draws, say, a net three or four percent of the vote away from the Republican nominee’s vote in a couple of key states, it could be enough to give a Democratic nominee the presidency.
After the primary season is over, Trump would likely run more as a centrist than a conservative, like other presidential candidates, and perhaps tone his theatrics down a notch.
At The Upshot Josh Barro argues that Trump is a moderate on some key issues. He has made vague statement of support for tax cuts and simplifying the tax code, but has so far refused to sign Grover Norquist’s tax pledge. Further,

The main way Mr. Trump stands out from the field on economic policy is leftward: While most Republicans favor free trade, Mr. Trump has called for much higher tariffs on imported goods to protect American industries from competition. He has also criticized his opponents for proposing cuts in Social Security, Medicare and Medicaid.
…..Instead of promoting his ideological purity, he notes that policy choices are circumstance-specific. For example, he’s not a priori opposed to single-payer health care. “It works in Canada,” he said at the first Republican presidential debate on Aug. 6. “It works incredibly well in Scotland.” Even in the United States, “it could have worked in a different age,” but it wouldn’t work very well right now, he said. So instead, he’d replace Obamacare with “something terrific,” which would take care of people who can’t afford health insurance.

Timothy Noah notes at Politico:

It was during Trump’s leftward drift in 1999 that he first proposed a wealth tax — a one-time 14.25 percent levy on fortunes more than $10 million that inequality guru Thomas Piketty might salivate over. “The concept of a one-time tax on the super-wealthy is something he feels strongly about,” Stone told the Los Angeles Times.
“He’s nothing if not inconsistent,” said Bruce Bartlett, a onetime tax aide to the late Rep. Jack Kemp (R.-N.Y.) who excoriated Trump’s wealth tax 16 years ago in the Wall Street Journal. “He’s been on every side of every issue from every point of view as far as I can tell.”

Trump has worked with unions in his business and generally avoids the snarling anti-union tone of many of his fellow Republican candidates. However, notes Noah,

But even in 2000, Trump had a low regard for teacher’s unions, who he wrote “blow smoke about professional this and academic that” and stifle competition by resisting school choice options. Trump would also appear to share fellow GOP candidate Scott Walker’s disdain for public employee unions in general, having donated $15,000 during Walker’s 2012 recall fight to the Wisconsin Club for Growth, which opposed it. “I believed what he was doing was the right thing,” Trump said…Trump parts with liberals in opposing an increase in the minimum wage…

Trump’s “leftward” credentials are more than a little compromised by his stated willingness to allow each state to formulate its own policies toward unions, rather than strengthen collective bargaining across the U.S., which many economists believe is needed to secure a thriving middle class. In substance, he is not so different than the others on the critical issue of restoring a healthy trade union movement. It’s ironic that Trump would take a moderate tone on any issues, including unions.
In a way, the Trump phenomenon is a test of just how far an in-your-face presidential candidate can go with policies that would disqualify other equally-‘moderate’ candidates with a less outrageous media profile. As Barro puts it

Mr. Trump is offering an unusual combination of extreme language, moderate policy and rudeness, and so far it’s connecting with Republican voters. Over the next few months, as voters learn more about Mr. Trump’s policy views, we’ll get to see which part of that combination is helping him soar, and whether his policy moderation and flexibility are liabilities.

Barro may be overstating Trump’s ‘moderation.’ It would be unwise to assume Trump would not vacillate again on his economic policies, since that’s been his pattern. His contradictions on policy make it hard to see how he could hold his own in a presidential debate.
But he has cleverly leveraged his outrageous media persona to catapult his candidacy to frontrunner status in the GOP, leaving his fellow presidential candidates flat-footed and unprepared. Most pundits still doubt he can win the Republican nomination — or the presidency. But If Trump can’t be the king, he could be a kingmaker.