The fact that Donald Trump wasn't willing to say he supports House Speaker Paul Ryan in the Wisconsin Republican's primary fight later this month is big news. This is a sort of political slam-dunk that Trump is refusing to execute.

But, if you closely read what Trump told WaPo's Phil Rucker about Ryan, there's something darker and more insidious going on here. It's not just that Trump isn't "ready" — his words — to endorse Ryan. It's that Trump is using Rucker to transmit a threat to Ryan: Start talking nice about me — or else.

Here's the relevant section of the interview:

RUCKER: Do you support Ryan?
TRUMP: Nobody has asked me if I support Ryan.
RUCKER: I’m asking now though.
TRUMP: I’m giving it very serious consideration.
RUCKER: To supporting Ryan?
TRUMP: Yeah.
RUCKER: But you haven’t decided?
TRUMP: No. I never said I’d support him. I’m giving it very serious consideration.
TRUMP: Just so you understand, his opponent is a big fan of what I’m saying. Big fan. His opponent who’s running a very good campaign obviously. You may have heard. His opponent sent me a very scholarly and well thought out letter yesterday. All I did was say thank you very much for your very nice letter.

That last comment is the most important one. After repeatedly emphasizing that his support for Ryan is an up-in-the-air thing, Trump makes sure to explain that Ryan's primary opponent — a man named Paul Nehlen — is a "big fan" of his. Also, apparently Nehlen is "running a very good campaign, obviously." (Nehlen had $176,000 in the bank as of July 20; Ryan had $9.5 million.) Also, Nehlen sent Trump a "very scholarly and well thought out letter." I'm convinced!

The message from Trump to Ryan is clear: Your opponent likes me and thinks I am great. You don't. Sure would be a shame if I had to go off and endorse him before the primary, wouldn't it?

That's as close to a public threat as you will get in politics.

Trump, never the subtlest of communicators, wanted to make sure Ryan didn't miss what he was up to in the WaPo interview. After discussing other topics, he, unbidden, asks Rucker this: "You want me to give you an exact quote on the Paul Ryan? You were asking." Trump would have been less obvious if he had broken down the fourth wall — pro-wrestling-style — and said something like: "I want to talk directly to Paul Ryan right now."

What follows is Trump reiterating just how on the fence he is about endorsing Ryan. He really could go either way on this one. He just needs some sort of sign (wink, wink, nudge, nudge). Here's the exchange

TRUMP: You want me to give you an exact quote on the Paul Ryan? You were asking.
RUCKER: Yeah, please do.
TRUMP: Okay, you’re asking me if I’m supporting Paul Ryan?
RUCKER: Yeah, if you’re supporting Paul Ryan.
TRUMP: I’m not quite there yet.
RUCKER: And why is that?
TRUMP: Just not quite there yet.
RUCKER: Has he asked for your support?
TRUMP: Everybody wants my support. You know why? Cause I had more than 14 million people that voted for me. And nobody gives us credit. There were 17 people in the race. I got more votes than anybody in the history of Republican politics. By millions. Don’t forget. How about if I had two people in the race? The number would’ve been twice as good. In other words, people with 2 million people. Because the Republican Party increased. [Trump looks at the TV.] That statement’s gotten a lot of play. I love that statement we wrote. So I’m just not quite there yet.

The most telling part of that back and forth is when Phil asks Trump why he's not at a place where he can endorse Ryan. "Just not quite there yet," Trump responds. Translated that means: He's not being nice enough to me yet — and he had better start if he knows what's good for him.

Ryan appears unintimidated. "Neither Speaker Ryan nor anyone on his team has ever asked for Donald Trump's endorsement," said campaign spokesman Zack Roday. "And we are confident in a victory next week regardless."