Bernie Sanders, left, stands with actor Tim Robbins, who introduced him at a campaign rally in Green Bay, Wis., on April  4. (Mark Kauzlarich/Reuters)

Tim Robbins is an actor who was very good in "Bull Durham." He's mostly known for playing Andy Dufresne in "The Shawkshank Redemption," but the role that best exemplifies his position in the present zeitgeist was his lead in "Bob Roberts." In that, he played a conservative candidate for the Senate who (spoiler alert) is revealed to the audience as a fraud when he taps his toes. It's a little heavy-handed.

Speaking of heavy-handed! Robbins appeared at a rally in Wisconsin on Monday on behalf of Democratic presidential candidate Sen. Bernie Sanders, where he made a weird analogy.

"After the Southern primaries," he said, "you had called the election" -- apparently referring to the media. "And who's fooling who? Winning South Carolina in the Democratic primary is about as significant as winning Guam. No Democrat is going to win in the general election. Why do these victories have so much significance?"

This is a not-uncommon argument among supporters of Sanders. Yes, Hillary Clinton is winning. But she's winning largely because she ran up big margins in Southern states. That, the argument goes, bodes poorly for the general, since those Southern states usually vote Republican.

This is a bad argument that borders on insulting.

First of all, South Carolina has a lot more people than Guam. Among the other bits of data one can point out about the 2016 Democratic primary is that Clinton has received far more votes than  Sanders -- 2.5 million more. Among those is a margin of about 175,000 more votes in the state of South Carolina, a margin that by itself is larger than the population of Guam.

Which means that Clinton came away from South Carolina with a net delegate haul of plus-25 -- she earned 25 more delegates than did Sanders. In the Democrats' proportional system, that's a big margin. It's a margin that Sanders has only managed once, in the Washington caucuses late last month. So in that sense, South Carolina matters a lot more than Guam.

As for the general election: Those of us who were paying attention in 2008 will remember that the same red-state critique was leveled at Barack Obama then. He was only really winning Southern states, Clinton's supporters noted, which spelled doom for the general election. That's really Robbins's point -- that winning South Carolina in the primary doesn't mean much for the general.

That's just rhetoric. Obama (who was endorsed by Robbins in 2008, mind you) didn't win South Carolina in the general election that year, but he crushed John McCain anyway. There's no need for a Democrat to win South Carolina. And besides, if the point is that you want a candidate that will only win narrowly contested general election states, the Democrats should embrace a candidate who wins in the populous, purple states of Florida or Ohio or Virginia. Which, in this primary, was Clinton and Clinton and Clinton.

Robbins's real point -- the real frustration of the anti-Clinton left -- is in that last statement. Why do these victories have so much significance? In other words: Why are these lopsided wins in the South so important, when Clinton and Sanders have played to ties in so many other places? And the answer is: because they helped Clinton build up a nearly insurmountable lead.

Sure, if you threw out the Southern states, Sanders would have a much better shot. But that's like saying that if you threw out cities in 2008, McCain would have beaten Obama. Sure! But that's not how it works. (Some Sanders supporters have suggested that the South got to vote first just to drive up that margin. Josh Putnam rebuts that here.)

There's also a strain of this line of argument that, in essence, is scoffing at the idea that black Democrats in the South greatly prefer Clinton. We've noted before that there's a strong correlation between the black turnout in a state and the results in the 2016 primaries. More black voters means a more likely Clinton win.

This is very tricky territory, of course, and I don't want to imply that the wish to dismiss Clinton's Southern victories is motivated by race. But there is often a sense that because Clinton dominated with black voters in the South that somehow makes those votes an anomaly -- as though those victories somehow don't represent the Democratic Party. Voters in South Carolina may not look much like the folks who came out to caucus in Washington, but their votes count. Those victories are significant because they were big wins in big states -- neither of which applies to Guam.

The fundamental disconnect for supporters of Sanders is that he's still running a real campaign and still raising more money than Clinton -- even though there's essentially no way he can win. We didn't say Sanders was done after South Carolina, but we did say it after Super Tuesday. Because the race was essentially over at that point, with Sanders having no real way to cobble together enough delegates to beat Clinton, barring a miracle.

And that's frustrating. It's frustrating to hear that your candidate can't win when it seems like he can win. Why are we so focused on those big wins in Southern states instead of the big wins Sanders enjoyed last week? Why isn't this still a tie?

The answer is: because of math. Because Clinton won a lot of big states by big margins, and even if Sanders were significantly more popular now than he was in February (which doesn't appear to be the case), that doesn't change the fundamental numbers.

Anyway. A bit of a rant only tangentially about Robbins's argument at Monday's rally. And a word of praise for the actor: Say what you will about Robbins, but he's certainly not afraid to go off-script.