Fox News host Bill O'Reilly joined Stephen Colbert on CBS's "The Late Show" on Monday, and the mood was, well, predictably tense. After all, O'Reilly (a.k.a. "Papa Bear") was a major inspiration for the conservative pundit caricature that Colbert used to play on his Comedy Central satire show, "The Colbert Report." Put another way: He was a constant target of mockery for years.

But the two were civil, if not warm, as they were when each appeared on the other's program in 2007. And at one point they got into a back-and-forth on federal spending that looked like a preview of a general election debate — especially if that general election pits Donald Trump (he of the military so strong and powerful we'll never have to use it) against Bernie Sanders (he of the free public college for all).

The exchange began as a discussion of O'Reilly's latest book, "Killing Reagan." O'Reilly was praising Ronald Reagan's military spending as essential in ending the Cold War when Colbert pushed back.

COLBERT: Ran up huge deficits though.

O'REILLY: He did, but it was in the pursuit of bringing down the Soviet Union, which was accomplished. Alright? So you bring down your major enemy, and you have to do it by spending money

COLBERT: But that's huge deficits that can be justified by military expenditure, but you're saying huge deficits cannot be justified by the humanities — by educating people, by the social services, the safety net. What's the difference to those things? They're both vital aspects of our culture. What is the difference between those two — why is one justified and not the other?

O'REILLY: This is a classic liberal position.

COLBERT: It's just a question. It's not a position. It's a question, Bill.

O'REILLY: No, it wasn't.

COLBERT: We have to be able to ask each other questions.

O'REILLY: I see.

COLBERT: We don't have to take sides. Why does it have to be liberal or conservative? Why can't we all just love each other, Bill?

O'REILLY: You're having a stroke again. Now, in self-defense, I think most people would agree ...

COLBERT: Am I attacking you? Self-defense?

O'REILLY: ... No, you have to spend money.

COLBERT: You do have to spend money.

O'REILLY: You have to defend yourself from an enemy who is bent on either conquering you or killing you. That's why we're in this war on terror now. On the arts and education, we have to get away from this fantasy that the government can solve all the problems by kicking money in. And we can't be promising everybody everything, as these pinhead politicians do constantly.

Here was the fundamental disagreement between Democrats and Republicans on the role of government, perfectly encapsulated in 90 seconds on a comedy show. Everybody is willing to spend money on something. There's just no consensus on what the priorities should be.