The rest of the Republican primary season should focus, almost exclusively, on whether Donald Trump is fit to be the next American president. And the main reason GOP voters should question Trump's fitness for holding that highest of offices — much less leading the party of Lincoln and Reagan — is that he's running a racially-charged, divisive, and disingenuous campaign. He's engaging in, as Mitt Romney rightly tweeted yesterday, a "coddling of repugnant bigotry [that] is not in the character of America."

Trump's policy views on, say, Medicare reform or top tax rates are secondary at best. His big idea, really, is that the basic answer to all of America's woes is the supergenius and negotiating prowess of Donald J. Trump. But looking at his agenda, as wispy and fantastical as much as it is, may give some clue as to the direction and substance of Trumponomics, should he win the Republican nomination and be elected president. And what he has proposed so far will hardly provide comfort to those who worry he's an unserious and unprepared candidate, at best.

A few examples:

Replacing ObamaCare: During the wonkiest moment of last week's GOP debate, Trump repeatedly and repetitively argued — to much mocking by Marco Rubio — that "we have to get rid of the lines around the states" so that there's more competition. Insurance companies could sell insurance according to the rules of whatever state they choose, and customers of any state could buy it. But few experts think that such a reform alone would do much to reduce costs or expand coverage in a post-ObamaCare world. Indeed, most center-right health-care plans include it as only one component of far more comprehensive reform. If "selling insurance across state lines" is the core of your ObamaCare replacement plan, then it roundly deserves to be mocked.

Tax cuts: Three organizations — Citizens for Tax Justice, Tax Policy Center, and Tax Foundation — have given budget scores to the Trump tax plan. And all find the plan would sharply reduce government revenue, with an average loss to government coffers of $11 trillion over the next decade. That's the main reason why a Center for a Responsible Federal Budget analysis of Trump's economic plan finds it would double the national debt over the next decade. Of course, the Trump tax cuts might well boost economic growth. But according to CRFB analysis, it would require the economy to grow as fast as 9 percent a year for a decade to make the Trump plan revenue neutral and 11 percent to actually balance the budget. Those are ridiculous numbers. Only very poor countries playing catch up, like China in the 1990s and 2000s, grow that fast. U.S. growth in the booming 1990s, by contrast, averaged 3.5 percent a year.

Mass deportations: Trump has promised to round up and send home some 11 million undocumented immigrants. The American Action Forum, a think tank led by former Congressional Budget Office boss Douglas Holtz-Eakin, has estimated it would take between $100 billion and $300 billion to arrest and remove them all, a 20-year process. Now if the price tag doesn't shake you, maybe this will: The Trump Deportation Force is also likely to vacuum up plenty of American citizens. An analysis by my AEI colleague Michael Strain suggests, conservatively, that perhaps 1 percent of total apprehensions would be in error. In other words, some 100,000 American citizens — about the same number of Japanese-Americans interned during World War II — would be at risk for deportation.

Now who knows exactly whether Trump intends to push such policies or whether they are merely negotiation starting positions. For instance, there is some reason to think his morally repugnant deportation plan is little more than strategic posturing in advance of some future negotiations. And it wasn't so long ago that he was talking about wealth taxes and single-payer healthcare, a completely different set of policy choices. Yet if Trump has no fixed core beliefs — other than those that will provide momentary political advantage — what exactly are Republicans voting for?