John Cornyn and other politicians say an incumbent should run in one of two ways: scared or unopposed.

Given that philosophy, Texas's senior senator is having nightmares about his 2020 re-election bid.

Nothing wrong with being scared, especially if it's early enough to stage the best campaign possible.

For Cornyn, running scared means being prepared.

He has already started his re-election bid, the earliest he's fired up his machine since beating former Dallas mayor Ron Kirk in 2002.

In December, he scored endorsements from fellow Texas Sen. Ted Cruz and Lt. Gov. Dan Patrick, moves that could inoculate him from a serious primary challenge from the right.

For years there's been talk that Cornyn, a fixture in Texas politics since his years as a Texas Supreme Court justice and attorney general, would at some point get a major challenge from a tea party conservative. It never happened.

Now Cornyn's biggest threat comes from Democrats, who will certainly mount a challenge. Last year former U.S. Rep. Beto O'Rourke came within 2.6 percentage points of beating Cruz, a finish that gave Democrats hope that a Democrat is closer than ever to winning the party's first statewide win since 1994.

After November's election, Cornyn said he was aware that O'Rourke could challenge him in 2020. And even if the El Paso Democrat opted instead for a run for president, he certainly would receive a significant challenge.

Sen. John Cornyn attends a ceremony to begin a period where President George H.W. Bush will lie in state in the Rotunda of the U.S. Capitol on Monday, Dec. 3, 2018, in Washington. (Smiley N. Pool / Staff Photographer)

Cornyn has called Cruz's near loss and the Democratic Party push in the midterm elections a "confluence of events" that served as a "wake-up call."

What's more, from 2007 to 2011 he served as chairman of the National Republican Senatorial Committee, getting a ground view of winning and losing campaigns across the country.

"We're thinking through this and trying to be prepared," Cornyn told The Dallas Morning News. "I can't predict for you what 2020 will be like, but we will be ready."

To that end Cornyn has already named a campaign manager. He's hired John Jackson, the Waco native who managed Texas Gov. Greg Abbott's successful election campaign against former Dallas County Sheriff Lupe Valdez. Though Abbott's margin over Valdez wasn't comparable to his 20-point victory over former state Sen. Wendy Davis in 2014, he helped turn out Republican base voters who helped not only Cruz, but other Republicans up and down the ticket.

Abbott was the only statewide Republican candidate with a significant field program. Cornyn hopes not to be caught without an organization to get voters to the polls.

"I'm thrilled to have John at the helm of my campaign," Cornyn said. "It's no secret national Democrats will again target our state and spend millions to wipe out conservatives in Texas. John's experience managing large field operations and building winning coalitions will ensure we're ready and help Republicans up and down the ballot."

Republicans like Cornyn's move.

"Hiring John Jackson was really smart," said political consultant Matt Mackowiak. "Melding the Abbott organization and the Cornyn organization would be good for up and down the ticket."

More than anything else, Cornyn will need campaign cash and a field operation to hold off a legitimate general election opponent.

Unlike the midterm elections, President Donald Trump, who has also started his re-election campaign, is on the ballot. Turnout in presidential election is higher for both parties, and since the election will be a referendum on Trump, Democrats could have more enthusiasm for the contest than Republicans.

Democrats are already talking about linking Cornyn to Trump, a strategy designed to drive independent voters away from him. In his previous re-election bids, Cornyn got healthy support from Hispanic and black voters.

But since the Texas electorate has more Republicans than Democrats, Cornyn would have the advantage in the general election, even if it's over O'Rourke and his stout fundraising.

Still, the closeness of the midterm contest also suggests Democrats can win in Texas, particularly if Republicans aren't prepared.

"If I were him, I would be worried," said Texas Democratic Party Chairman Gilberto Hinojosa. "The 2020 numbers will be unprecedented in the history of Texas. ... He's got to be worried that he may be serving his last term in the U.S. Senate. Maybe he should have asked Trump for a Cabinet appointment."

But Mackowiak said Cornyn would be fine in 2020, adding that Cruz's tough race signaled the urgency of the situation for Texas Republicans.

"Obviously this last election was a wake-up call for Republicans," he said. "I really don't believe Cornyn is vulnerable, but it doesn't mean the race won't be competitive."