For state Democrats, the question is whether to help front-runner Hillary Clinton maintain her Southern "firewall" in Super Tuesday primaries or assist Sen. Bernie Sanders in breaching it.
Trump, Cruz and Rubio, along with three super PACs, are hoping to influence voters' choices with a last-minute, statewide TV ad blitz. Some Rubio ads feature Republican Gov. Bill Haslam, who unexpectedly endorsed the Florida senator last week.
Neither Kasich, who was in Nashville on Saturday, nor Carson, whose wife, Candy, is expected to speak for her husband at Lee University in Cleveland on Monday, are running ads.
Clinton, who will be in Nashville today after her smashing victory in South Carolina's Democratic primary Saturday, is airing ads, but there have been few if any from Sanders, who appears to be retreating north of the Mason-Dixon line.
Trump is set to visit Memphis today, and Rubio is scheduled to appear with Haslam in Knoxville on Monday.
Tennessee is one of 11 states participating in GOP Super Tuesday primaries. A six-state subset dubbed the "SEC primary" comprises mostly Southern states like Georgia and Alabama that have college football teams in the Southeastern Conference.
Democrats are holding primaries in 11 states (a few states are different from Republicans).
Any Tennessee Republicans who doesn't think their votes vote count may want to consider this: The 58 GOP delegates at stake here represent the third largest number among the 11 Super Tuesday states. It's nearly 10 percent of the 595 up for grabs.
"I remember elections where it was long decided before it ever got to the Tennessee primary," said Hamilton County Republican Party Chairman Tony Sanders.
"Being up early like it is absolutely raises the state's profile. It's going to be an important vote; you can see that by how much effort people are putting in."
The same goes for state Democrats, with Tennessee accounting for 67 of the 865 Democratic delegates up in their states.
So how are things going to shake out here in the GOP primary? Tennessee public polling has been sparse. Only two surveys are public.
Trump is seen as the front-runner, but long-time observer Bruce Oppenheimer, a Vanderbilt University political science professor, isn't making any bets.
"Things are moving in his direction," Oppenheimer said of Trump, "but it's not over yet. And the question is, can that get turned around. Primaries are very hard to gauge. Voters are volatile and it's very hard to figure turnout."
The last poll - nearly five weeks ago from Middle Tennessee State University - showed 33 percent support for the brash billionaire businessman. That's compared to 17 percent for Cruz, a U.S. senator from Texas; 5 percent for Rubio, 7 percent for neurosurgeon Carson and a blip for Ohio governor Kasich.
A Republican strategist told the Times Free Press on Friday he has seen newer polls showing Trump at about the same level while Rubio and Cruz were both at about 15 percent.
Clinton, endorsed by a number of party stalwarts including the Tennessee Legislative Black Caucus, led Sanders, an independent and self-described democratic socialist, in a recent survey by Public Policy Polling, a Democratic firm. Clinton led 58 to 32 percent - a 26-point spread.
Clinton's dies to Tennessee go back at least 25 years through her husband, former Arkansas governor and president Bill Clinton.
"I would think Hillary is going to win in Tennessee," Oppenheimer said.
Cruz should have the upper hand here. The Christian conservative and tea party favorite has a solid Tennessee campaign organization and hits religious and constitutional values. Those strategies helped Mike Huckabee and Rick Santorum to Tennessee primary victories respectively in 2008 and 2012.
But Trump has been picking off those voters to gain pluralities in the New Hampshire and South Carolina primaries and the Nevada caucuses.
Tennessee Lt. Gov. Ron Ramsey, the Republican Senate speaker, is "absolutely surprised" by Trump's popularity, especially among religious conservatives.
"I do think Trump has become a force that's going to be practically impossible to stop now," Ramsey told reporters last week.
"It's amazing to me to watch [Trump]," added Ramsey. "The guy has a very foul mouth. I'm sure he's not exactly been a regular church attender to say the least."
Still, he noted, "Polls will show you that people are fed up with Washington, D.C. I think people are saying he's got his faults, he's got his warts, but it beats what we've got now. That's the only way you can explain it."
Robin Smith of Hixson, a former Tennessee Republican Party chairman not publicly backing any of the campaigns, said Trump's rise "doesn't surprise me."
"Even back when I was chairman I remember making kind of a statement that loyalty to party was beginning to dilute itself down. And people were very frustrated.
"I think that frustration now has reached volcanic proportions and we're seeing the unintended consequences of not listening to voters," Smith added.
Clinton is expected to draw significant support from women and black voters.
In 2008, blacks accounted for roughly a third of Tennessee Democratic primary voters in exit polling, according to The New York Times' website. That year, Clinton carried Tennessee over Barack Obama in the primary.
Among Clinton supporters is state Rep. JoAnne Favors, D-Chattanooga, who said she's admired Clinton since her years as first lady in the 1990s when she fought for national health care.
A member of the Black Caucus, Favors noted her district includes whites as well as blacks. Clinton's support, she added, extends well beyond the black community.
"She's a very intelligent lady and she understands the needs of all levels of people," Favors said. "I think she would be an effective administrator. Having been secretary of state, that's pretty awesome."
One thing puzzling observers, especially Republicans, is that no candidate launched television ads to take advantage of Tennessee's two-week early voting period.
Some 375,000 Tennesseans cast early ballots, including 250,000 in the GOP primary. Some Republicans estimated a third or better of the GOP electorate has likely already voted.
Here are voices of some voters who cast early ballots:
"Our country's in bad shape," said John Harrison, a white voter and DuPont retiree from Hixson. "We need somebody that will stand up for the people, look out for our safety."
Harrison voted for Rubio, calling him "well-qualified" with a "level head."
Julie Adams, 67, is another white retiree from Hixson. Although she's a lifelong Republican, she said,"Washington is so corrupt, I am sickened on a daily basis."
She described herself as "totally a Trump fan, in spite of all his faults - he owes nobody anything so he can actually work for the people."
Deena Williams, 77, another white retiree from Hixson, also likes Trump for paying his own way.
"I think this election is critical," Williams said. "Our country has been going down the tubes for the past eight years. If it's not saved now, with this election, I don't know what's going to happen."
But H.J Evans, 67, described Trump as "boisterous rude - he's not your typical candidate."
She and her husband, Tom Evans 72, said they voted for Kasich. "We feel he's more able to work with others, and he still has a chance," Tom Evans said.
Nancy Clemmer, 55, and her mother, Lucy Coppedge, 76, are white voters who both said they voted for Sanders.
Coppedge said she has been active in politics "a long, long, long, long time."
"I don't trust Hillary," she said. "Bernie has been around almost as long as I have. I believe like Bernie believes."
Clemmer believes the Republican candidates have bamboozled the voters and said of Trump, "They're hearing his bluster. There's no substance what he is saying."
Brenda and Curtis Benn, both black voters from Brainerd, said they voted for Clinton.
"The country is about to change totally," said Brenda Benn, a seafood manager at a local grocery store. "You want to make sure the leadership has the same values and outlook you have to take the country forward.
The couple said they like Clinton for her intelligence, experience, compassion and communication.
"She's dealt with them, she's bargained with them. She's not a stranger to how to handle the different Cabinets. She's just got a lot of experience. She's been there and done that," Brenda Benn said.
The mention of Donald Trump's name set off Curtis Benn, a 71-year-old retiree.
"That's the craziest man I ever saw!" he exclaimed as his wife tried to shush him. "If they get that man in there, we're all going to hell."
Contact staff writer Andy Sher at asher@timesfreepress.com or 615-255-0550.