The Democratic nomination is now Hillary Clinton's to lose.

Bernie Sanders still has time to mount an improbable comeback. But, barring any political earthquakes, Clinton's sizable delegate lead and broad coalition make it difficult to imagine how Sanders can pull off an upset, according to close trackers of the race.

"Clinton has been the huge favorite this whole time and continues to be," said Kyle Kondik, managing editor of Sabato's Crystal Ball at the University of Virginia's Center for Politics. "I don't see how Sanders catches up to her."

On Super Tuesday, Clinton surged ahead of Sanders by the metric that matters most: delegates. She racked up 505 delegates in winning seven of 11 states, compared with the 334 delegates Sanders took in winning four states, according to an analysis by Richard Berg-Andersson, a researcher who tracks Democratic delegate math at the Green Papers. (Some districts remained too close to call as of Wednesday morning.)

"Clinton had the night she needed to have," Berg-Andersson said. "She's now well on her way to winning the nomination."

Why Super Tuesday was mostly bad for Bernie Sanders

Clinton now leads Sanders by around 200 pledged delegates — in large part because of her big wins across many Southern states on Tuesday.

It's tough to see how Sanders closes that gap, even if he runs more or less evenly with her the rest of the race. That's in part because the Democratic Party awards delegates proportionally, meaning candidates need to win the popular vote by big margins to make up a delegate deficit.

Beyond the delegate math, Super Tuesday provided several other reasons to doubt that Sanders could seriously threaten Clinton for the nomination.

Perhaps the biggest reason is that Clinton has continued to clobber Sanders among African-American voters, and not just in the Deep South. She won a massive 93 percent of the black vote in Alabama, for instance, but also won black voters in Oklahoma, Virginia, Texas, and Tennessee by huge margins.

There had been some speculation that Sanders had closed the gap with Hispanic voters in Nevada. But as FiveThirtyEight's Harry Enten notes, Clinton won Hispanic voters by around 42 points in Texas — suggesting Florida and New Mexico will also be favorable terrain for the former secretary of state.

Then there was also evidence that Sanders's appeal is limited even among white voters. Sanders lost Massachusetts, even though white people made up 86 percent of the electorate; he also lost the white vote in Tennessee, Texas, Georgia, and Virginia, according to NBC News's exit polls.

Sanders's biggest problem: Where does he rack up delegates?

The problem for Sanders isn't just that Clinton swept the Southern states. It's also that she's likely run well ahead of him in primaries with big Democratic establishments that loom large on the calendar.

"I think Massachusetts was the most telling win of the night," said Elaine Kamarck, senior fellow and director of the Center for Effective Public Management at the Brookings Institution. "In a place that's in Bernie Sanders's backyard and known for its liberalism, she still won."

Clinton's strength in Massachusetts, which she won narrowly, probably reflects her strength in states with strong Democratic institutions. And that suggests she'll have a huge advantage when the contest reaches delegate-rich states like Pennsylvania, Ohio, Illinois, and New York.

"Those are areas with large African-American populations and an established Democratic Party organization that will be very Hillary-friendly," Berg-Andersson said. "Sanders is not going to get delegate boosts from those states."

By contrast, the kinds of states where Sanders has done well don't tend to have that many delegates.

A big piece of Sanders's coalition has been downscale white voters, who helped him win Oklahoma by 10 points on Tuesday. But while there are many states that fit this demographic makeup, most of them just aren't very big and don't have that many delegates. (Added up, the Sanders-friendly states like Kansas, Nebraska, Idaho, Wyoming, and Oregon have around the same number of delegates as Clinton-friendly Illinois.)

None of this is to say that Sanders is certainly done. Sanders's campaign argued on Wednesday that Sanders has a viable path to the nomination that runs through industrial Midwestern states battered by the recession, according to the Washington Post.

That strategy would make the March 8 primary in Michigan, which has 147 delegates, a crucial battleground for Sanders. "We still think we have a winning hand in this game, and we’re going to continue to play it," said Tad Devine, a Sanders aide, according to the Washington Post.

But with Clinton leading by double digits in several recent national polls, Sanders will have to change something — and do it fast — to alter the fundamentals of the race.

"[Clinton] has a substantial lead, a substantial delegate lead, and a great deal of momentum," Kamarck said. "I suspect she's going to win. But it's not impossible for him to come back."