Opinion writer

Republican presidential candidate Donald Trump speaks at a caucus night watch party at the Treasure Island Hotel & Casino in February in Las Vegas. The New York businessman won his third state victory in a row in the “first in the West” caucuses. (Photo by Ethan Miller/Getty Images)

Donald Trump is running for the Republican nomination, and while he leads in delegate and popular vote it is worth looking into how he is winning. It may not be because he’s won over a plurality of the hearts and minds of Republicans.

Some smart numbers crunchers point out that Trump has won all open primaries (Alabama, Arkansas, Georgia, Massachusetts, Nevada, New Hampshire, South Carolina, Tennessee, Vermont and Virginia) with the exception of Minnesota and Texas. (Texas is Sen. Ted Cruz’s home, of course.) When it comes to closed primaries, however, Trump’s record is much spottier. He has won a grand total of two states — and by single digits (Louisiana by 3 and Kentucky by 4).

What is more, when you look at those open primaries won by Trump, in most the turnout was very high for Republicans, but was down significantly from past years in the Democratic race. In Alabama, for example, GOP turnout was up over 300,000  from 2008 while Democratic turnout was down about 138,000 from 2008. In Georgia, Democrats were down nearly 300,000 from 2008; Republicans were up roughly 329,000. South Carolina, Tennessee and Virginia show a similar pattern. This might suggest voters from the Democratic primary, not brand-new Republican voters, are showing up. And remember about 65 percent of them were voting for someone other than Trump.

This makes sense since Trump and Sen. Bernie Sanders (I-Vt.) have a certain overlap in appeal (poor whites who think trade with China is killing jobs, voters who hate President George W. Bush, populists hostile to free markets and suspicious of Wall Street). Ideological arguments have limited appeal to Trump voters because so many are not conservative or even Republican.

That leaves us with several takeaways.

First, when Trump claims a popular mandate from Republicans, his opponents may be able to make a convincing case that it’s Democrats and independents who make up a large share of his vote, leaving his accumulation of Republican support looking less impressive. When and if it comes to an open convention, it might be that other candidates have a stronger mandate from specifically Republican voters.

Second, if Trump is the nominee, will those cross-over primary voters stick with Trump? The ones who voted for Ohio Gov. John Kasich or Sen. Marco Rubio (R-Fla.) may go right  back to the Democrats. And even the ones who voted for Trump because of his anti-trade message or sense he is on their side may find Hillary Clinton far more compelling.

Finally, we are going to enter a stretch with lots of big-delegate states with closed primaries. California (172), Connecticut (28), Florida (99), Pennsylvania (71), New Jersey (51) and New York (95), for example are all closed primaries. Just those six states have 516 delegates.

This is not to say Trump has failed to get a lot of Republican votes. He has. But some of his wins are due in significant part to Democrats, whose mandate the RNC convention is not obliged to respect and who are not necessarily going to stick with Trump in a general election. It should also give his Republican challengers a lift knowing that delegate-rich states without the Democrats and independents he has been relying on are coming up. As the next few weeks play out, we will see just how well Trump can do without his security blanket of non-GOP voters.