As he lagged in the GOP presidential primary polls, Paul felt forced to defend his decision to run for president in a January op-ed in the Lexington Herald Leader, pointing out that he has maintained a near-perfect voting record, unlike some of his fellow senators running for president.
"I am running for president for the same reason I am your senator: to fight for you, for our country and for our rights," he wrote. "We don’t yet know where that will take me, but as others look at running for Senate against me, I want to remind them, and you, that I have done my job well, done it with Kentucky in mind, and done it exactly how I said I would do it."
Even so, Paul's reelection bid didn't seem likely to be a tough race. Democrats struggled to find a viable opponent after watching two of their top candidates get beaten in races they thought they could have won in recent years — Adam Edelen in the 2015 state auditor race, and Secretary of State Alison Lundergan Grimes in a 2014 Senate race against Senate Majority Leader Mitch McConnell (R-Ky.).
But in the waning day of Paul's presidential campaign, Democrats found a high-profile candidate: Jim Gray, mayor of Lexington.
Now, as Paul ends his presidential run and turns his eyes back toward Kentucky, his reelection appears to be no sure thing.
"I do think that enough of the Kentucky electorate is up in the air that Rand Paul cannot assume that he can regain his Senate seat," said Stephen Voss, a political science professor at the University of Kentucky.
Here's the breakdown of pros and cons for Paul's reelection bid:
PRO: Kentucky has been Republican at the federal level for some time, and it's swinging red at the state level as well. Some in Kentucky view the surprise November election of tea party Gov. Matt Bevin as the beginning of the end of Democrats' mostly decades-long hold on the office. In March, we find out if Kentucky's statehouse, the last Democratically held one in the south, will also be in Republican hands.
CON: After losing much of their bench in November's elections, Democrats finally found an opponent. Gray is Lexington's first openly gay mayor and has a record and profile that may excite his base. Gray has personal money to spend from his family's construction business. And his small business background is a plus in a conservative-leaning state. Gray, unlike Democrats' last Senate candidate, Grimes, hasn't tried to hide some of his progressive views, which put Grimes in an awkward situation. Grimes wouldn't say whether she voted for President Obama, for instance; Gray already said he has.
PRO: Even though it didn't go as planned, Paul's presidential campaign kept him in the national spotlight, potentially boosting his name recognition outside Kentucky and in it. And while Paul said plenty of things Democrats can dig through, he made it through without any major gaffes. He even had a victory of sorts in temporarily halting the National Security Agency's mass phone collection program. Even if his presidential campaign was doomed, "I'm not sure on balance you'd say that effort hurt his Senate chances," Voss said.
CON: Perhaps with an eye on the White House, Paul has never really tried to be a traditional senator. From the moment he got to Washington in January 2011, he threw himself into national security issues and headline-grabbing filibusters, skipping over some of the less-sexy things that Kentucky constituents might appreciate, like building up his office and focusing on constituent services. Paul is just not the ribbon-cutting kind of senator, and it's unclear whether voters in Kentucky will hold that against him.
PRO: Kentucky Democrats are weakened after two big electoral blows. Before Nov. 3, Kentucky Democrats used to control five statewide offices, including the governor's office. Now, they control just two. And one of those statewide office holders, Grimes, lost the 2014 Senate race by more than 15 points. Some observers say Kentucky is experiencing a decades-overdue political realignment to match up with the rest of the heavily red South, and there's not a lot Democrats can do to stop it.
CON: He didn't win any friends among state Republicans by having the state party switch from a primary to a caucus. He promised to fund the cost of the switch out of his own pocket, so that his name would only appear on the ballot once: For Senate, Republicans would hand him the GOP nomination for president in a caucus. Republicans did agree to move to a caucus, but somewhat begrudgingly. Now that you could argue the drama was all for naught, Paul may have burned some bridges in the state he'll need to get reelected.