Updated at 12:40 p.m. with quotes from Dallas-area senators and at 3:45 p.m. with news of David Whitley's resignation and at 6:02 p.m. with comments from Gilberto Hinojosa.

AUSTIN — Interim Secretary of State David Whitley - who oversaw a botched investigation that questioned the citizenship of nearly 100,000 Texas voters - is officially out of a job.

Gov. Greg Abbott appointed Whitley, a former top aide, to the position in December after the previous secretary of state resigned. But just before lawmakers finished the 2019 session Monday afternoon without confirming him, the embattled elections chief resigned "effective immediately."

"I am forever indebted to Texas for all it has done for my family and me," Whitley wrote, according to the letter, which was first published by the Austin-American Statesman. "Thank you again for this incredible chance to make it a better place."

The resignation officially ends his short run as the state's top voting official. Abbott can now choose a new secretary of state, who can serve in the role until the Legislature reconvenes in 2021.

Democrats pounced after Whitley's resignation, proclaiming it a victory for voting rights in Texas.

"It was long overdue for David Whitley to vacate his office and now it's time for Gov. Abbott to appoint a new secretary of state who will respect our democracy and our great state," said Gilberto Hinojosa, chairman of the Texas Democratic Party.

Usually a perfunctory act, Whitley's nomination became a flash point this session after his office questioned the citizenship of nearly 100,000 Texas voters. Facing steep pressure from voting rights advocates, Democrats in the Texas Senate had said they could not vote to confirm Whitley because of the botched investigation. The caucus stuck together during the session despite significant political pressure to drop their opposition.

"The reality is Democrats showed solidarity on that issue because of Whitley's position on voter suppression. That was the issue. It was not that he was not a good person. It seems like he was a great person," Sen. Royce West, D-Dallas, said after the news broke of Whitley's resignation. "You've got to have a secretary of state that will be fair and balanced."

Whitley's short tenure was controversial from the beginning.

In January, just a month after he was chosen, Whitley issued an advisory claiming that approximately 95,000 people who identified themselves as noncitizens when applying for a driver's license at the Department of Public Safety also appeared on the state's voter rolls. About 58,000 of them had voted in one or more elections since 1996. Whitley's office sent letters to county election administrators urging them to investigate the names on the list for possible voter fraud.

But critics quickly pointed out a flaw in the advisory’s logic: People could have become U.S. citizens between the time when they applied for a driver’s license at DPS and when they registered to vote. (Noncitizens who are in the country legally can be issued a driver’s license in Texas.) Driver’s licenses last for six years, and state laws do not require people to return to update their license if they become U.S. citizens before the expiration.

Within days of the advisory's release, state officials were quietly calling counties to tell them their initial lists were flawed and included people who had already proved their citizenship to DPS. In Harris County, more than half of the 30,000 names on the state-provided list were placed there in error. In McLennan County, all of the people on the list were citizens.

Three high-profile lawsuits against the state followed. Some counties that had begun carrying out investigations after the state's advisory also were named as defendants.

In court, state officials said at least 25,000 people on the initial list had been placed there erroneously and had already proved their citizenship. Many counties across the state refused to investigate the names on their lists until they received new data from the state that did not include the initial errors.

The state settled the dispute in late April, agreeing in court filings to rescind the advisory and to recast the way it would investigate whether noncitizens were voting in the state so that no citizens were swept up in the probes. The state also agreed to pay plaintiffs $450,000 in attorney fees.

Whitley's confirmation required the support of two-thirds of senators, or 21 of them if all 31 are present. The Senate's 19 Republicans supported the governor's nominee, but without any Democrats crossing over, his confirmation seemed mathematically impossible.

That didn't keep him from trying. Days after the court settlement, Whitley asked to meet with Senate Democrats, but they did not appear to change their minds.

"The damage is done," Sen. John Whitmire, D-Houston, the longest-serving member of the chamber, said in April, echoing a sentiment expressed by the leader of the Senate Democratic Caucus, Sen. José Rodríguez of El Paso, in February.

Sen. José Menéndez, D-San Antonio, said Democrats would have lost the trust of their voters if they broke ranks and approved Whitley.

"My constituency has lost confidence in the secretary of state," he said last week.

"The credibility that the caucus has would be called into question if we didn't stand strong," Menéndez said, adding Republicans in the GOP-dominated chamber would have confirmed him already if they could. "If they had a way to do it, they would have already done it."

The blocking of Whitley's confirmation is a surprising show of strength from Senate Democrats, who have been on the losing side of a Republican supermajority in the chamber for several years and have been mocked by political observers as a doormat for the state's Republican leaders.

The three Democrats representing D-FW, two of whom ousted Republicans in November, said their ability to stick together and block Whitley's nomination shows "elections matter."

"Together as a caucus, we reinforced our opposition in the face of political pressure," Sen. Nathan Johnson of Dallas said Monday. Fellow freshman Democrat Sen. Beverly Powell of Burleson said she hoped their newfound political clout "motivates our citizens to use their voices at the ballot box."

"This is the first time, in a long time, that the [Senate] Democratic Caucus has stayed together on an issue that so affects the Democratic Party," West, who's represented Dallas in the Senate for a quarter century, added. "This bodes well for us in the future in terms of turning Texas blue."

Abbott stood by his nominee, working behind the scenes to convince some Senate Democrats to back Whitley. He even took the unusual tack of deflecting some of the blame on the Department of Public Safety, home of the heralded Texas Rangers, and director Steve McCraw.

The governor’s loyalty to Whitley was not surprising. He was considered part of “the Abbott family” and had worked for him for nearly a decade and a half, starting when he graduated from the University of Texas in 2005. Whitley, 36, worked for Abbott while he was the attorney general and continued as he began pursuing a law degree at UT in 2009.

The Alice native followed Abbott to the governor's mansion and became his deputy chief of staff, earning $205,000 last year before being nominated for secretary of state.