As we move to Nevada, the third contest on the Democrats' primary calendar, the picture of who the Democrats will nominate for president is as clear as mud. Here's what we do know: Bernie Sanders and Pete Buttigieg lead the delegate count (22 for Buttigieg to 21 for Sanders), the Elizabeth Warren and Joe Biden campaigns are running on fumes, while Amy Klobuchar is hoping to translate her third-place showing in New Hampshire to success in states where she has a much smaller footprint. But, what everyone is talking about this week is the person not on the ballot until March 3; former New York City Mayor Mike Bloomberg.

Bloomberg gambled that he could wait until this late in the game because: 1) the four early states contain few total delegates; 2) Biden would turn out to be a weak frontrunner; 3) Bernie Sanders and/or Elizabeth Warren would rack up wins and delegates and would be hard to stop once Super Tuesday came and went. All three have come to pass. Team Bloomberg also knows that while the other candidates in the primary have to depend on momentum and media narrative to carry them from February to March, he can use his deep pockets to build that base of support.

To give you a sense of how big of a media footprint Bloomberg has put in the Super Tuesday states, I asked Advertising Analytics (thank you Gates DePodesta!) to track media spend (broadcast, cable and digital) in the 14 states that vote on March 3. From December 19 until February 13, Bloomberg has spent over $121.5 million on media in those states. The only other candidate who has made any signficant media buys in Super Tuesday states is Sanders, who has spent about $9.7 million. Tom Steyer has dropped more than $20 million in California, but little elsewhere.

As we wait to see if Bloomberg's money advantage can indeed buy love/delegates, it's also worth checking in on the other media obsession of this week: a contested convention. How did we get to the, "Oh my God, no Democrat will have a majority of the delegates by the convention" stage so quickly?

First, the collapse of one-time frontrunner Joe Biden has left a huge void in the moderate/non-Bernie lane. No one is that surprised that Biden turned out to be a mediocre to weak candidate. What was surprising – and consequential – was that it took until voting started before this became apparent. Second, the unexpected collapse of Elizabeth Warren. The fact that the one-time frontrunner failed to perform well in two states that are tailor-made for her candidacy (Iowa and New Hampshire) does not bode well for her in states like Nevada and South Carolina where she is not as well-established.

This has given Sanders the ability to coalesce his base, while the rest of the candidates are dividing the other non-Bernie votes. Add in proportional voting, and the prospect of Bloomberg dividing the pie even more, and it's not hard to see the possibility of the primary season ending with no candidate able to amass a majority of the delegates.

One of the biggest criticisms of the Sanders campaign (one I've written about as well) is that he has a high floor but a low ceiling. He's taken 26 percent of the vote in both Iowa and New Hampshire, enough to get him a win and a second-place finish, but not enough to dominate the delegate haul. If he can't expand much beyond 26-27 percent, can he win the nomination? Can anyone?

To help walk me through this question, I reached out to my favorite delegate guru, Josh Putman of the Frontloading HQ website. "I remain bearish — at this time — about a contested convention," Putman told me. He says that while he understands all the reasons for the chatter about such a prospect, he argues that "there are some additional institutional facets that do insulate the process to some extent against the threat of a contested convention."

The first is the 15 percent threshold. If a candidate doesn't hit 15 percent of the vote, he/she doesn't get any delegates. In New Hampshire, for example, just Sanders, Buttigieg and Klobuchar hit that threshold at the state and congressional district level. As such, they were the only candidates to get delegates. Sanders, however, is more likely to hit that 15 percent threshold in more states than any of the other candidates. Unlike Buttigieg and Klobuchar, Sanders has strong support from voters of color. And, he can also put together a coalition in overwhelmingly white states. Four Super Tuesday states, Massachusetts, Vermont, Maine and Minnesota, look a lot like New Hampshire and Iowa. Plus, unlike the other non-Bloomberg candidates in the contest, Sanders has a dedicated stream of small-dollar fundraising dollars that are impervious to the latest polling data, or even a loss.

Plus, says Putnam, "there is some additional math to consider." Even though Sanders took just 26 percent of the total vote in New Hampshire, "he won almost 38 percent of the total delegates. That's because the denominator is not the total vote, but the total qualifying vote (just the votes of those over 15 percent)." In other words, Sanders' ceiling is higher than the total popular vote would suggest. That only holds true, of course, if there are multiple candidates splitting up the vote and only three or so picking up at least 15 percent.

Even so, Putman acknowledges, "it remains true that a candidate wants to start approaching 50 percent of the total delegate vote sooner rather than later, so winnowing is going to have to occur whether actual or operational." In other words, a candidate who fails to hit 15 percent in multiple contests is going to have a tough time staying in the race for very long. At some point, the money coming into the campaign dries up.

And, while we are all laser-focused on the next two states up on the calendar — Nevada and South Carolina — the states that vote between Super Tuesday and St. Patrick's Day will provide us with some more concrete answers. By March 18, two-thirds of all delegates will have been awarded from vote-rich states like Texas, California, Ohio, Illinois, Michigan and Arizona. "Bottom line," Putnam told me, "at this point, it is too early for a freak out. When Democrats shed their green after St. Patrick's Day, they may or may not actually feel green. But that is the point when they will know with more certainty what the end might look like."

For now, however, Sanders looks as well-positioned as he's ever been. But, as the field narrows, he's got to prove he can expand his base. Meanwhile, if Buttigieg/Klobuchar/Biden fail to impress in Nevada and South Carolina, it will be up to Bloomberg to prove that he can turn the Democratic nomination fight into a mano-a-mano contest between he and Sanders.