Ryan Zinke, the Interior Secretary, called the top Democrat on an environmental committee a drunk on Twitter Friday, after the lawmaker wrote an op-ed saying Zinke should resign amid several corruption allegations.

“It’s hard for him to think straight from the bottom of the bottle,” Zinke wrote in a statement. “This comes from a man who used nearly $50,000 in tax dollars as hush money to cover up his drunken and hostile behavior. He should resign and pay back the taxpayer hush money and the tens of thousands of dollars he forced my department to spent investigating unfounded allegations.”

Zinke’s attacks are directed at Rep. Raul Grijalva, who as the top Democrat on the House Committee on Natural Resources, will soon be in a position to investigate the Department of Interior for a number of ethics scandals, including allegations of nepotism against Zinke.

The interior secretary appears to be referencing a case in 2015, when Grijalva arranged a “severance package” of more than $48,000 for a top female aide who allegedly threatened to sue him for being intoxicated and creating a hostile work environment. The case was reported by the Washington Times in 2017. In 2018, the Office of Congressional Ethics reviewed the allegations and found no evidence to support the claim that the staffer was paid inappropriately, and dismissed it.

Grijalva published an op-ed in USA Today Friday, calling on Zinke to step down immediately, promising to “intensify” inquiries into the departments possible ethics violations. He writes:

It’s worth recounting how far that abuse went on Republicans’ watch. As has been widely reported, an Interior Department inspector general investigation of Mr. Zinke — one of at least 17 publicly known formal probes of either him or his department since he took office — was recently referred to the Justice Department. The referral centers on a land development project called 95 Karrow in Mr. Zinke’s hometown of Whitefish, Mont., involving David Lesar, the chairman of oil contractor Halliburton; his son John; and a Montana property developer named Casey Malmquist. The proposal would increase the value of land controlled by Mr. Zinke’s family.

For months, Zinke has been under scrutiny for alleged ethics violations, including reports of private flights, and reports that he reassigned Native American senior career staff in the department and doesn’t think diversity is important.

But Zinke, a former House Republican, didn’t take kindly to the Democrats’ fighting words, responding with a personal attack against Grijalva — who’s been known to be a regular at a Capitol Hill neighborhood bar, Tune Inn.

Grijalva responded to Zinke on Twitter, saying the interior secretary was only “resorting to personal attacks” because the allegations of corruption are credible and serious.

The allegations against Secretary Zinke are credible and serious. Instead of addressing the substantive issues raised in this morning’s op-ed, he's resorting to personal attacks. https://t.co/QRiVPAjxPv — Raul M. Grijalva (@RepRaulGrijalva) November 30, 2018

In the past, Grijalva has denied that the severance pay for his former staffer was in anyway related to sexual harassment.

“On the advice of House Employment Counsel, I provided a severance package to a former employee who resigned. The severance did not involve the Office of Compliance and at no time was any allegation of sexual harassment made, and no sexual harassment occurred,” Grijalva told the Washington Times in 2017.

Outside an apparent personal feud between two former House colleagues, this episode is telling of what will likely be an acrimonious relationship between top Democrats in Congress and members of the Trump administration.

House Democrats have already promised to investigate every aspect of the Trump administration — from the president’s finances and his campaign’s alleged ties to Russian nationals to his cabinet members’ alleged ethics violations. Addressing corruption and government accountability are Democrats’ top priorities going into 2019.

“The election results were about clean government as much as any particular policy choice, and the next Interior secretary will be watched as closely as the one before,” Grijalva wrote in his op-ed.