“McCaul has put himself in a good position to be toward the top of the list of people who might succeed Sen. Cornyn," a source close to McCaul told The Texas Tribune. "He's built statewide name recognition and a political effort that could be quickly turned on for a statewide campaign for Senate."
There was a similar readout on the Democratic side.
"If there’s a special election called, Joaquin would strongly consider that," a source close to Castro told the Tribune of a would-be Senate vacancy.
“He’s already running for Senate, and ... if an election came up for a Texas [U.S.] Senate [seat] before that, he would undoubtedly look at it," a source close to O'Rourke told the Tribune. "There’s no question he would take a look at it.”
O'Rourke is currently running against U.S. Sen. Ted Cruz, as the junior senator aims for a second term in 2018. The O'Rourke source did not elaborate on what these deliberations might mean for the 2018 race.
The Senate vacancy is a serious possibility: Cornyn met with his former Senate colleague, U.S. Attorney General Jeff Sessions, on Saturday afternoon at the Department of Justice headquarters to interview for the job, according to news reports.
Should Cornyn leave the Senate, Gov. Greg Abbott would appoint a placeholder, and then the state would hold a special election several months later.
The political calculations for Castro and McCaul — both men of stature within their party caucuses who've mulled Senate runs in the past — are a little different. A special election would allow each man a free pass — a chance to run without vacating their House seats.
McCaul considered running for the Senate in 2012, and again last year in what would have been a primary challenge to Cruz. McCaul is chairman of the U.S. House Homeland Security Committee, and he could be on deck for the gavel at the House Foreign Affairs Committee once he is term-limited out of his current leadership role.
Castro recently passed on a challenge to Cruz after a lengthy deliberation process.
In his previous deliberations, Castro had to weigh leaving behind his climbing rank within the U.S. House — he's a deputy whip within his caucus, and he is racking up seniority as a member of the House Foreign Affairs Committee.
But more than anything, Castro in recent months has become a high-profile party spokesman on the investigation into the 2016 Russian cyberattacks on the U.S., thanks to his assignment on the House Intelligence Committee.
The positioning in the GOP field is highly volatile and involves a different calculation.
In the event of a vacancy, it is assumed Abbott would appoint a Republican, which could — or could not — clear the nomination field for the special election. Senate hopefuls are both gaming out who might be his pick, and whether that person would be a weak enough primary candidate to challenge in a special election.
Since Friday morning, political insiders across the state have weighed the different scenarios and contenders. But actual Republican contenders are fairly quiet — for the time being.
A key consideration for many GOP contenders is the 2012 Senate race. A number of high-profile Republicans passed on running for retiring U.S. Sen. Kay Bailey Hutchison's Senate seat, out of a fear of then-Lt. Gov. David Dewhurst — only to see the once-unknown Ted Cruz take the nomination.
This could be a second chance for ambitious GOP politicians eyeing the Senate. And the same circumstances as Castro would also apply to Republicans: They can run in this special election without risking their current seats in the congressional delegation or in state government.
Despite the Democratic interest, this is still a likely hold for the Republicans. No Democrat has won a statewide race since 1994.
All the speculating aside, there are no assurances this race will come to pass: Cornyn is one of around a dozen serious contenders for the FBI post.
Correction: A photo caption initially identified U.S. Rep. Beto O'Rourke as a Republican. He is a Democrat.