But he didn't stay close on Tuesday.

Even if he'd won or does win Missouri -- which still hasn't been called -- and even if he'd won Illinois and Ohio, it wouldn't have mattered -- unless he won big. Hillary Clinton won big in North Carolina and Florida, helping add to her delegate margin. Sanders needed big wins in some states to keep it close. He didn't get big wins -- if he got any.

What was a big Clinton delegate lead became a massive one. The below doesn't include superdelegates, the unpledged delegates that cause so many complaints. This is earned delegates, the people committed to Clinton and Sanders through voting. Clinton's lead over Sanders is now 2.7 times the biggest lead Barack Obama had over her at any point in 2008.

This isn't insignificant. Because the Democratic calendar features only proportional contests -- no winner-take-alls -- it means that Sanders can't simply win a California and make up a big chunk of that gap. He needs to win big states big.

In order for Sanders to pull even with Clinton in pledged delegates, he'd need to win 57.8 percent of the remaining delegates -- meaning, essentially, that he'd need to win about 57.8 percent of the vote in every remaining state, on average. And once you include superdelegates -- who heavily favor Clinton -- in order to close the gap he'd need to win more than two-thirds of the delegates that are left.

He's won some states big, certainly. But the states in which he's dominated include Vermont, a small state without many delegates. Where vote totals are available, he's gained 66 delegates against Clinton in states where he's won with 57.8 percent or more. In states where he's earned 42.2 percent of the vote or less -- the margin to which he needs to hold Clinton -- he's at a 296-delegate deficit. Clinton is running up the margins with big wins in bigger states.

Can Sanders win? Sure. Who knows what will happen over the next two months. Hillary Clinton's support could completely collapse and Sanders could easily roll up huge margins in every state. Possible.

But there's no indication that's going to happen. That was the key lesson from Tuesday night: Nothing has changed in the calculus for the two candidates. His surprise win in Michigan looks, in light of Ohio and Illinois, more like a fluke than a predictor of how the rest of the contests would go. (That fluke, incidentally, only left Sanders essentially tied with Clinton in the state for delegates.) If Sanders went into Tuesday needing a big performance, he leaves needing a miracle.