Three weeks ago, there were three Democrats and 12 Republicans running for president, all of whom were tied at zero votes nationally. Since then, we've bid farewell to candidates who weren't able to solidify support from moderates (Chris Christie and Carly Fiorina) or who couldn't line up the evangelical vote (Rick Santorum and Mike Huckabee) or who couldn't get any support from anyone (Martin O'Malley, Jim Gilmore).

It's only been 10 days since the New Hampshire primary, but it feels much longer, as though the past week's conventional wisdom has already stiffened into a status quo. After this weekend's voting, though, we can expect a new batch of wet concrete. And here, for your reading pleasure, are some possible molds into which it can be poured. (I apologize for that extensive analogy.)

When the Republicans vote in South Carolina

Did Donald Trump hold his lead? As we noted Friday morning, Donald Trump should win the South Carolina primary. He's leading in every poll, often by a wide margin.

If the gap narrows significantly, it could suggest that some polls showing a tighter race nationally have captured an early shift against Trump. If the race is very close -- within a few points -- it will again raise questions about the ability of Trump's campaign to actually turn out his voters. More on this below.

Did Ted Cruz turn out evangelicals? Ted Cruz has two bases of support that overlap: evangelical voters and conservatives. In Iowa, Cruz's win was boosted by winning a third of the evangelical vote -- a group that made up two-thirds of the voters.

Cruz's campaign hinges on his ability to run a smart campaign that gets his supporters to the polls. South Carolina has a large population of evangelical voters, a group that made up 65 percent of the vote in 2012. If Cruz can keep pushing those voters to the polls -- and keep leading with them -- it bodes well for Super Tuesday on March 1, when a number of southern states with large evangelical populations go to the polls.

How did conservatives and moderates vote?

Trump and Marco Rubio get support across ideological groups, as recent polling from the New York Times and CBS News makes clear. Ted Cruz gets more support the further right you move on the spectrum and John Kasich gets more support the more you move to the left.

Trump's broad support means that he is often running neck-and-neck with Cruz among conservative voters. Does that hold up in South Carolina? And, if not, what does that suggest about states moving forward?

On the moderate end, a new poll from South Carolina shows Jeb Bush surging past Kasich for those votes. That's not a big part of the electorate in South Carolina, but if Bush can become the preferred moderate candidate, it makes it more likely that he (and not Kasich) will get to keep powering through the primaries.

Of course, Kasich, Bush and Rubio are all unlikely to drop out before March 15, when Ohio and Florida go to the polls -- the home states of all three. (Editor's note: I disagree with Philip about Jeb staying in the race if he can't get into the top three in South Carolina.)

Did new voters show up at the polls? Trump's support is disproportionately among people who haven't participated in caucuses or primaries before. This is his value proposition: He'll bring new voters to the polls.

If new voters don't come to the polls, though, it suggests again that Trump's campaign struggles with getting out the vote. And if he struggles with that, it means lots of close races in the future could shift toward his opponents.

Does Ben Carson drop out? Carson will almost certainly finish in fifth or sixth place. He's not going to win the nomination; it's not clear he'll win any states. Why's he (still) running?

When the Democrats caucus in Nevada

How did the nonwhite vote break out? This is the most important question, by far.

Hillary Clinton is poised to win South Carolina next week. The close race in Nevada, the first state on the calendar with a decent-sized nonwhite population, suggests that at least among Hispanics, Clinton's advantage may not be very big.

This is the first state where polling of voters will be able to break out how white voters compared to nonwhite voters since there will be a statistically significant number of the latter. If Sanders is able to stay close with those groups while dominating with white voters, that's a good sign for him long-term.

Did Bernie Sanders turn out young voters? Sanders has a giant advantage with younger voters -- a group that doesn't turn out as much. Like Trump's issue with new voters, Sanders needs to keep turning out young voters as a counterweight to Clinton's advantage with older voters -- a group that turns out much more frequently.

In Iowa, younger voters turned out far less than in 2008, when they powered Barack Obama's win in that state. Sanders needs to do better.

How liberal was the electorate? Democrats have been identifying as liberal much more strongly in recent years. In Iowa, the voting population was much more liberal than in 2008, and that's a group that supports Sanders more heavily.

If Nevada also skews more heavily liberal, that may suggest that liberal turnout will continue to be high in primary states -- good news for Sanders.

Were the late polls accurate? This is an interesting question for 2020. We noted this week that Nevada polling was off pretty badly in 2008, and that there wasn't much of it this year. It will be interesting to see if pollsters did better with their late polls -- polls that generally suggest Clinton should win.

Whether Clinton wins or loses is relatively immaterial moving forward. It's the underlying trends that will give us a sense of where the race is headed more than the top-line results. As a reminder, there was a candidate who lost all four of the earliest primary contests and six of the seven Super Tuesday matchups but still won the nomination.

That was Bill Clinton.