Because in just the last six days Trump has been all over the place on fiscal issues that are central to Ryan's approach to conservatism. Trump wants to dramatically lower taxes for everyone, including the nation's wealthiest. But wait, no, he actually wants taxes for the rich to go up! But, no, he doesn't want that either!
Instead, what he meant to say was that his big tax-cut proposal is just a starting point and that he will negotiate with Congress on rates that will be higher than what he initially proposed but lower than they are now. For everybody.
And then he pulled the ultimate Trump. Those who reported that I want to raise taxes for the rich were wrong, he claimed. But this is what he said on NBC's "Meet the Press": "I may have to increase it on the wealthy — I'm not going to allow it to be increased on the middle class." He later said: "The rich is probably going to end up paying more."
How do you misreport that?
And then basically he gave up the game to The Wall Street Journal. He really has no core beliefs on taxes. "I always believe in flexibility," he said, "and remaining flexible."
Trump also caused great consternation and confusion on CNBC last week when he appeared to suggest he would negotiate deals with America's creditors if the economy goes bad to pay less than we owe. That sure sounded to people like what companies do in bankruptcy and what countries like Greece and Argentina do when they are nearing collapse.
But no, no. Trump reappeared Monday morning to say, of course, he would not try to make creditors take haircuts on U.S. debt. That would be insane! Instead he would look to buy back debt when prices drop. Fine. We do that. But he couldn't leave it there.
"This is the United States government," Trump said. "First of all, you never have to default because you print the money, I hate to tell you."
This once again terrified Wall Street and conservative policy professionals. Of course the Fed prints money and it can have the effect of lowering debt burdens. But presidents never suggest we try to inflate our way out of debt problems. Because once again that is the province of failed economies like Argentina in the late 1990s. Never mind that Trump was heedlessly blundering into monetary policy that is the province of the Federal Reserve.
The Fed, both publicly and most of the time privately, operates outside the influence of politicians usually interested in short-term popularity rather than long-term economic health. A president heading into office on the record as saying the Fed can just bail us out of debt would be deeply disturbing to global markets. It's also the complete opposite of conservative policy that favors spending cuts and economic growth to ease debt, not financial engineering.
Part of the problem with Trump is that he doesn't really care about policy, he cares about winning. And part of the problem is that he goes on so many TV shows so often and rambles on about anything and everything that it's incredibly difficult to pin down where he is on any issue. He could take three different positions within the same news cycle or event in the same interview. He is the king of the word salad.
So Ryan will be looking for some core beliefs, some animating principle other than the acquisition of power that makes Trump want to be president. And Ryan will want to hear how Trump plans to reverse his historically high negative ratings with women and minorities.
But most of all, Ryan, who could wind up skipping the Republican convention he was supposed to chair, will end up asking if Trump is even remotely conservative on trade, taxes and spending. Because at the moment, Trump appears likely to run on these issues as a more liberal version of Hillary Clinton.
— 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.