Full vetting of a presidential nominee’s financial holdings can take “weeks,” or even “sometimes months” in the case of extremely wealthy individuals, according to the head of the federal watchdog agency responsible for identifying and resolving nominees’ potential conflicts of interest.

Walter M. Shaub Jr., director of the Office of Government Ethics, said the length of the process varies depending on the nominee’s responsiveness to questions, the complexity and extent of his or her financial holdings, and the time it takes the nominee to consider and agree to steps that OGE identifies as necessary to resolve conflicts.

“It usually takes even the most responsive nominees time to gather the information they are required to produce, particularly if they are wealthy,” Shaub wrote in a letter to Sen. Patty Murray (D-Wash.) on Monday. “Some nominees also find it difficult to untangle their complex financial investments and employment arrangements quickly, especially if they wish to do so without incurring otherwise avoidable financial losses.”

Shaub’s letter, including a detailed explanation of the process OGE goes through to examine nominees’ financial holdings, came in response to Murray’s inquiry about the status of the office’s ethics review of Betsy DeVos. DeVos, President-elect Donald Trump’s pick for education secretary, is a Michigan billionaire and one of several wealthy Trump nominees whose confirmation hearings had been scheduled for this week despite unfinished OGE ethics reviews.

Democrats had sought to delay DeVos’s hearing, scheduled for Wednesday, citing her incomplete ethics review and the potential for unknown or unresolved conflicts of interest. Late Monday night, Murray, the ranking member of the Senate Education Committee, and Lamar Alexander (R-Tenn.) issued a joint statement announcing that the hearing had been postponed until Jan. 17 to accommodate Senate scheduling issues.

Sean Spicer, incoming White House press secretary, told reporters Tuesday that DeVos has submitted all required information to the ethics office.

In his letter to Murray, Shaub — who has been outspoken about his concerns that the GOP is rushing confirmation hearings without allowing the ethics office to complete its work — did not reveal anything specific about the status of DeVos’s ethics review, citing nondisclosure rules.

But he wrote that a nominee cannot officially file his or her ethics report until the OGE is satisfied that financial disclosures are complete and that the ethics agreement — which could require the nominee to resign positions or divest holdings — resolves any potential conflicts. And he emphasized that nominees are required to file those reports before their hearings.

“The requirement to obtain OGE’s certification before a hearing invariably provides the necessary leverage to secure the cooperation and legal compliance from nominees,” Shaub wrote. “Of course, that leverage is greatly diminished if a hearing is held before OGE’s preclearance and subsequent certification.”