Here's what to watch on what's sure to be a Super Saturday -- with a few notes on the Maine Democratic caucuses and the Puerto Rico Republican primary that follow on Sunday, as well:
Saturday's contests offer Cruz one major tactical advantage.
A crucial component of Trump's strength has been his ability to expand the Republican electorate -- shattering turnout records in states like Virginia and bringing into the fold "Reagan Democrats" in northern states.
But those contests were open. To participate, registered voters don't have to be registered members of the GOP -- they could just walk in on election day.
Republicans have held four contests that were closed: Iowa, Nevada, Oklahoma and Alaska. And Cruz, not Trump, won three of the four.
The most important factor to keep in mind Saturday: Kansas, Kentucky, Louisiana and Maine's contests are all closed.
That makes Saturday an immediate test of Cruz's long-term viability. If he can win as many states as Trump, it'll bolster his argument that he is the logical alternative to the front-runner -- particularly if those two are the day's only winners.
Clinton's Southern sweep
She's already won South Carolina
, Texas, Virginia, Georgia, Tennessee, Alabama and Arkansas.
Now, Clinton is looking at Louisiana -- followed by Mississippi on Tuesday -- to close out the Deep South.
Her strength among African-American voters has helped her run up huge margins of victory across the South so far, and Saturday should be no different.
Her campaign isn't conceding Kansas and Nebraska, either. Wins there would show she can expand the map, shutting Sanders out of states with whiter electorates and caucuses, rather than primaries -- events that tend to favor well-organized activists further to the party's left.
Saturday's results might not shake up the delegate count in the Democratic race.
But they will set the tone for three intense days in Michigan, where Clinton and Sanders will meet for a debate Sunday night in Flint and follow it up with campaigning through Tuesday's primary.
Rubio in Louisiana
The Bayou battle pits Trump's strength among Southern Evangelicals against Cruz's ability to win with rock-ribbed conservatives in a state that neighbors Texas -- just like he did in Oklahoma on Super Tuesday.
So Rubio is staring at a likely third place finish in a state with 46 total delegates at stake.
But what he's really seeking is to reach 20% support -- no matter where he finishes.
It's the latest challenge for a Rubio campaign that has to fight to keep from dying from 1,000 tactical cuts. In Louisiana, candidates must win at least 20% of the vote statewide to qualify for any of its at-large delegates. \
Rubio wants to avoid the problem he faced in Texas and Alabama on Super Tuesday: Because he didn't reach that same 20% threshold that those two states also require, he was nearly shut out of the delegate race -- a big part of why Cruz has nearly double the delegates Rubio has accumulated so far.
Presidential contests aren't just about racking up the most state wins and the strongest finishes. They're a long slog through complicated delegate apportionment rules. And right now, those rules are working against Rubio.
He'll have an opportunity to win a bunch back on March 15, when Florida holds its 99-delegate winner-take-all contest. But if he's shut out between now and then, his path to the 1,237 delegates it takes to win the nomination might disappear.
Go West, Sen. Sanders
The next two Tuesdays will be tough for Sanders.
First, Michigan and Mississippi vote. Then, on March 15, Florida, Illinois, Missouri, North Carolina and Ohio hold their primaries.
Sanders will put up a fight, particularly in the Great Lakes states.
But his real opportunity to rack up wins and delegates comes when the race moves west in late March and early April, with states like Arizona, Utah, Alaska, Washington, Wisconsin and Wyoming on the calendar.
How will he fare there? Keep a close eye on Kansas and Nebraska on Saturday for the first hint.
Sanders is likely to fall further behind in the delegate count over the next two weeks, so he'll need to show he can not only win western states, but run up big margins, to keep up his argument that he should stick it out until late April, when New York and then a swath of liberal, east coast states vote.
Sanders could also celebrate Sunday, when Maine holds its Democratic caucuses. He's already won next-door New Hampshire and Vermont.
The runaway Trump train
After 10 wins in 15 contests, Trump looks increasingly difficult to catch.
He expects another strong showing in Maine, where he could replicate northern wins in New Hampshire and Vermont and possibly even surpass 50% -- which would give him all of the state's 23 delegates.
And he could also win Kentucky, Kansas and Louisiana.
He'll face a stiff challenge from Cruz in states like Louisiana and Kansas, and Rubio could best him on Sunday, when Puerto Rico holds its 23-delegate Republican primary.
But national polls show Trump is blowing out his opponents -- and that's exactly what he'll need to keep doing.
Increasingly, Republicans like Mitt Romney who are determined to stop Trump are pushing to support his strongest foe in each state -- no matter who that foe is.
So he needs victories big enough to keep anyone from stopping him, even at the Republican National Convention.
Saturday -- just like Super Tuesday -- gives him opportunities to win all over the map.