He has a few core proposals that unite his coalition thus far and would seem likely to remain his focus through November, including renegotiating the terms of foreign trade, deporting immigrants here illegally, building a wall along the Mexican border and blocking Muslim refugees from entering the United States.
The rest looks fuzzy or fungible or both. His tax plan includes a large cut in the corporate rate and the top marginal income tax rate — but he has spoken favorably of raising taxes on the rich. He has promised to spend more on the military and on infrastructure, and not to touch Social Security benefits, but he also has said he would pay off the entire national debt in the course of eight years. Virtually no policy analyst believes those goals are compatible.
His health care plan strings together a series of conservative proposals to inject more free-market competition into the system, in hopes of expanding coverage and reducing prices. But he has, in the past, embraced universal government-directed coverage.
Here’s a synthesis of what we know about where he says he would lead the country. (Note: This is an expanded and revised version of a similar post published last year, with more details about the policies Trump has put forward throughout the long GOP campaign.)
On economic policy, there are a couple of crucial differences between Trump and the rest of the Republican Party. For one, Trump opposes the trade deal President Obama is negotiating in the Pacific, arguing the agreement will put American manufacturers at a disadvantage. He's also said he thinks Japan is manipulating the price of the yen to help exporters there, and the deal should include language on currency manipulation.
GOP policymakers generally agree with Obama on the importance of free and expanded trade, and Republicans in Congress voted in favor of pursuing the Pacific agreement.
Ted Cruz, however, shares Trump's position. The senator from Texas, who suspended his presidential campaign after Trump defeated him in Indiana on Tuesday, at one point supported the bill to give Obama expanded authority to pursue the agreement. He changed his position, though, and voted against it.
Another difference of opinion is on Social Security. Republicans have long sought to partially privatize the program or to make benefits less generous, arguing it is fiscally unsustainable. Trump, however, has said he would defend the program as it exists.
"I will do everything within my power not to touch Social Security, to leave it the way it is," Trump said at a debate in March in Miami.
In an interview in 2011 with Sean Hannity of Fox News, Trump seemed to suggest that Social Security does need to be reformed, but that endorsing adjustments to the program would be too risky politically. "You have to deal with it," he said, but a moment later, he seemed to change his position.
"The Republicans have to be careful not to fall into a Democratic trap," he said. "I'm protecting the seniors. The seniors are in a certain way the heart of this country, and I'm protecting the seniors."
Trump's proposal on taxation is similar to the standard plan offered by GOP nominees over the past several elections, and he has won the endorsement of leading supply-side economists, including Arthur Laffer, a former adviser to President Ronald Reagan.
Despite his populist rhetoric in favor of taxing the rich, Trump's proposals would reduce their taxes. His plan would set the highest marginal rate on individual income, currently almost 40 percent, at 25 percent, and he would reduce the rate on corporate income from 35 percent to 15 percent.
Trump would also reduce taxes for the poor. One notable feature of his plan is that those who would be exempt from paying any income tax — individual taxpayers with incomes less than $25,000 — would receive an additional, one-page form from the Internal Revenue Service with a space to write the words, "I win."
Overall, though, Trump's plan would mainly benefit the rich. The nonpartisan Tax Policy Center projects that the changes he's proposed would increase the incomes of the poorest one in five Americans by 1 percent on average, while increasing the incomes of the richest one in five by 9.7 percent.
Trump has pledged to repeal the Affordable Care Act, President Obama's health-care reform. His proposal calls for making it easier for insurers to market policies across state lines, encouraging people to save money for health-care expenses in tax-exempt accounts and converting Medicaid into an annual grant to be administered by state governments.
Trump has also said repeatedly that the government should have more leeway to negotiate better prices for drugs prescribed to Medicare beneficiaries, and that by doing so, the government could save as much as $300 billion a year. The government only spends about $78 billion a year on prescriptions, however.
Probably the most profound disagreements between Trump and other Republican leaders are on matters of foreign policy.
In an interview with The Washington Post's editorial board, Trump questioned U.S. alliances with nations around the world, saying that they have been too costly and that the benefits are uncertain. He has said that Saudi Arabia should receive less in aid from the United States, and that the U.S. military presence on the border between North Korea and South Korea places an unfair burden on U.S. taxpayers.
He also said that the United States might have to reduce its financial commitments to the North Atlantic Treaty Organization. "NATO is costing us a fortune, and yes, we’re protecting Europe with NATO, but we’re spending a lot of money," he said.
Given these views, some experts who have advised previous Republican candidates on foreign policy have said they will vote for Hillary Clinton, the Democratic frontrunner, instead of Trump.
What Donald Trump is doing on the campaign trail
Like many other leading Republicans, Trump reject the consensus among climatologists, which is that climate change
and that it is
Gay rights and gender
Trump has said he supports "traditional marriage."
"What do you say to a lesbian who's married, or a gay man who is married, who says, 'Donald Trump, what's traditional about being married three times?' " Jake Tapper asked Trump on CNN's "State of the Union" earlier this year. (Trump's current wife, Melania, is his third.)
"I really don't say anything," Trump eventually replied. "I'm for traditional marriage."
The frontrunner, however, has more moderate views on the debate over transgender rights. He has objected to a new law in North Carolina requiring people to use public restrooms for the gender listed on their birth certificates, suggesting it goes too far. "Leave it the way it is," he said last month. "People go, they use the bathroom that they feel is appropriate. There has been so little trouble."
The GOP candidates in this campaign uniformly oppose abortion, and as of 2011, Trump is no exception. That was when he abandoned his previous support for reproductive rights.
"People change their positions all the time, the way they change their wives," Michael Cohen, special counsel to Trump, told National Journal at the time.
Trump is generally opposed to gun control. After the terrorist massacre in Paris in November, he said that fewer people would have been killed had French gun-control laws been less strict and more civilians had been able to return fire.
"It would have been a much, much different situation," Trump said. "You look at certain cities that have the highest violence, the highest problem with guns and shootings and killings — Chicago is an example, toughest gun laws in the United States, nothing but problems."
Trump's views on this topic are well-known. "People are flowing into this country by the millions, not by the thousands, by the millions, and destroying the fabric of the country," Trump told Iowa radio host Steve Deace earlier this year. "They're bringing drugs. They're bringing crime. They're rapists," he later said of Mexican immigrants. He also told The Post that as president, he would erect a wall along the Mexican border, which he said "would be very effective" in deterring immigrants from entering the country.
"A wall is better than fencing," he said. "It's more secure. It's taller."
Contrary to Trump's claim that millions of people are entering the country, the data suggest that more people are leaving than entering the country across the southwest border, and the population of undocumented immigrants has been falling since 2007. Additionally, immigrants are less likely than the population as a whole to commit crimes, research suggests.
Finally, one of Trump's most divisive proposals has been to temporarily ban any Muslim foreigners from entering the United States. A poll conducted by The Post and ABC News in December found that 59 percent of Republicans supported the idea, while just 36 percent of the general public agreed.
Trump's position on monetary policy has been inconsistent. In the past, he has argued that the Federal Reserve's efforts to stimulate the economy would cause inflation and that any improvement in stock prices was just an illusion. "From a stock standpoint, you're creating basically false numbers. You're devaluing the dollar," he said in 2012.
In fact, inflation has been subdued for the past seven years, remaining well below the Federal Reserve's target of 2 percent. Some economists even argue that target should be raised.
In October, Trump said again he thinks that the central bank's accommodative policies were "a political thing," adding that the Federal Reserve's Janet Yellen "is keeping rates too low, too long." In an interview with The Post last month, he forecast economic calamity as a result of these policies.
"I’m talking about a bubble where you go into a very massive recession, hopefully not worse than that, but a very massive recession," Trump said. "Look, we have money that’s so cheap right now. And if I want to borrow money, I can borrow all the money I want."
A couple of weeks later, however, Trump complimented Yellen on doing a "serviceable job."
Correction: An earlier version of this post misstated the results of an analysis of Donald Trump's proposal by the Tax Policy Center, giving the center's estimates of the effective tax rates under the plan rather than change in income after taxes. This version has been corrected, and we regret the error.