DALLAS (AP) — The FBI recently opened a criminal investigation into claims that Texas Attorney General Ken Paxton abused his office to benefit a wealthy donor.

The probe, which was confirmed to The Associated Press by two people with knowledge of it who spoke on the condition of anonymity because the investigation is ongoing, marks an escalation in the latest controversy to surround the high-profile Republican, who has spent years under indictment on unrelated state securities fraud charges.

The FBI's interest in Texas' top law enforcement official arose from a rebellion by Paxton's top deputies, who accused him of breaking the law by using his office to help a wealthy donor with a troubled real estate empire who also hired a woman with whom the married Paxton allegedly had an affair.

Paxton has broadly denied wrongdoing and refused calls to resign, saying he'll seek a third term in 2022 and that he's prepared to fight it out in court. He has weathered other storms during his rise to becoming one of the country's leading legal crusaders for conservative causes.

With the complex drama likely to continue, here is what you need to know about Paxton's cases:

WHAT IS PAXTON'S BACKGROUND?

Paxton, a 57-year-old lawyer, was a Texas legislator before he became the state attorney general in 2015. His wife was later elected to his former state Senate seat representing Dallas suburbs.

An evangelical conservative, Paxton has positioned himself as a fierce fighter for right-wing causes and close ally of President Donald Trump. He has sued to overturn the Affordable Care Act, to end an Obama-era program that protected young immigrants from deportation, and to limit mail-in voting during the coronavirus pandemic.

He has also been dogged by ethics questions for much of his public life and spent most of his tenure as attorney general maintaining his innocence in the face of securities fraud charges. Paxton pleaded not guilty to three felony counts in 2015 and narrowly won reelection three years later.

His lawyers and allies have successfully stalled the fraud case for years and it remains unclear when or where he might stand trial.

WHY IS THE FBI INVESTIGATING PAXTON?

In the runup to this month's election, Paxton's top deputies riled Texas politics by accusing him of breaking the law to help businessman Nate Paul.

Seven senior lawyers in Paxton's office reported him to the FBI in late September, accusing him of abusing his office, bribery and other crimes. The group included some of Paxton's longtime allies and was later joined by the agency's head of law enforcement. All eight have since resigned, been put on leave or been fired, prompting a whistleblower lawsuit.

The full extent of what Paxton’s employees told the FBI is unknown and the agency has consistently declined to comment.

Paxton’s actions appear to have helped Paul in at least four ways. But the one that led his staff to report him was Paxton's hiring of an outside lawyer to investigate Paul’s claims that the FBI, federal judges and others were conspiring against him.

The lawyers in Paxton’s office felt Paul’s claims were unsupported and outside of their office's jurisdiction. The Houston lawyer Paxton hired had no prosecutorial experience but did have ties to Paul’s defense attorney.

Paxton has largely not responded to questions, but he said there's nothing to the claims against him.

WHO IS NATE PAUL?

Paul is an Austin-based developer in his early 30s who owns properties valued at more than a billion dollars. His grip on this empire has come into question because of delinquent debt and spiraling legal problems.

Last year, the FBI raided Paul's offices and palatial home. An FBI document obtained by the AP suggests the investigation is focused on potential securities fraud.

Paul has not been publicly charged with any crime and alleges that FBI agents, a federal judge and others broke the law during the searches. In another request for a criminal investigation that reached Paxton's office, Paul claimed businessmen and another judge were conspiring to steal $200 million worth of his properties.

WHAT CONNECTS PAXTON AND PAUL?

In Texas, most criminal cases are handled by local prosecutors. Paxton's unusual move to take up Paul's complaints raised red flags for his deputies and questions about the friendly relationship between Paxton and Paul.

Paul gave Paxton $25,000 during his 2018 reelection campaign, but the full nature of their ties remains unclear.

A significant connection came to light when Paul said in a deposition this month that he'd hired a woman at Paxton's recommendation. Paxton acknowledged having an extramarital affair with her in 2018, when she was a state Senate aide, two people told the AP. They spoke on the condition of anonymity due to fears about retaliation.

Paul said he didn't hire the woman as a favor to Paxton, who hasn't denied the affair happened.

Paxton suggested in a statement that he took on Paul's case because it's what Texans expect.

“I make no apologies for being a fierce investigator and defender of individual rights in the face of potentially unreasonable and authoritarian actions,” Paxton said. “Doing so is not favoritism.”

Paul's lawyer, Michael Wynne, has lambasted Paxton's office for bungling the investigations and suggested that Paul might sue.

WHAT'S NEXT?

Paxton's office dropped the probe of Paul's complaints in October after the allegations against the attorney general became public and local prosecutors expressed concern.

Since then, information has dribbled out in the press and various lawsuits against Paul. That trickle could turn into a geyser if the former employees suing Paxton are able to take depositions and obtain records through discovery.

But FBI investigations often take months or years and normally become public only if someone is charged.

The controversy hasn't turned Paxton's party against him. Gov. Greg Abbott and other Texas Republicans expressed initial concerns about the allegations but have remained silent for weeks and have exerted no public pressure on him to resign.

During next year's legislative session, lawmakers could move to censure or impeach Paxton. But the latter is rare in Texas and the attorney general has a defender in his wife, state Sen. Angela Paxton.

For now, Paxton is telling “the citizens of Texas” that he'll continue to advocate for them — including in his own court cases.

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Follow Jake Bleiberg: https://twitter.com/jzbleiberg