WASHINGTON — Last week, a senior Justice Department official told reporters that they'd decided not to open a criminal investigation into President Donald Trump’s July call with the Ukrainian president because they couldn’t “quantify” Trump’s request for dirt on former vice president Joe Biden as a “thing of value.”

But the Justice Department hasn’t always required a specific price tag to press charges under criminal laws that refer to “things of value,” court records show. Federal prosecutors have brought cases in the past under theories that sex, government information, witness testimony, worthless stock, and more are, legally speaking, “of value.” States and federal courts have found that “amusement,” a promise to reinstate an employee, and an agreement not to run in an election all count as well.

And former special counsel Robert Mueller wrote in his final report earlier this year that campaign opposition research voluntarily offered to a campaign — say, dirt on a top Democrat running against you — would likely be a “thing of value,” although he noted no court had ruled on that so far.

It’s against the law for a candidate to ask for or accept “money or other thing of value” from a foreign national. But that law and others that also refer generally to things “of value” don’t provide a clear definition of what the term means. It’s been up to judges — and, in the case of campaign finance enforcement, the Federal Election Commission — to weigh in.

The chair of the FEC has taken issue with the Justice Department’s interpretation of “things of value,” and there’s at least one complaint pending before the FEC accusing Trump and his allies of violating campaign finance laws by asking Ukraine for help.

Trump, meanwhile, has continued to ask foreign governments for help attacking a political rival — on Thursday, in front of television cameras, he called on China, along with Ukraine, to investigate Biden and the candidate’s family.

Luke Cass, a former federal prosecutor with the Justice Department’s Public Integrity Section, said the Justice Department had taken a broad view of “things of value” in other types of criminal cases, such as bribery prosecutions, but it rarely came up in campaign finance cases.

“How do you calculate the value of dirt? It’s challenging. What if it turns out there’s nothing negative about the information provided, then it has no value and is worthless?” Cass said. “You have to prove the case beyond a reasonable doubt. … I guess the department’s decision was a recognition of that burden with a statute that’s seldom used and not the clearest.”

Paul Seamus Ryan, vice president for policy and litigation at government watchdog group Common Cause, called the Justice Department’s position “absurd.” Common Cause filed a complaint with the Justice Department and FEC claiming Trump, Rudy Giuliani, and others allegedly involved in soliciting information from Ukraine violated the foreign contribution ban.

“There is no doubt in my mind that a competent prosecutor could prove beyond a reasonable doubt to a jury that an investigation by the government of a foreign country … is a thing of value in this context,” Ryan said.

Any violation of the foreign contribution ban can lead to a civil enforcement action by the FEC or be considered an impeachable offense by Congress, Ryan said. For the Justice Department to prosecute it as a crime, the government would have to show the violation was willful and that the “thing of value” exceeded $2,000 for a misdemeanor charge, or $25,000 for a felony.

Ryan said he didn’t think it would be hard for prosecutors to at least meet the $2,000 line when it came to political opposition research. Cass agreed that prosecutors only had to show that the “thing of value” met the minimum thresholds, as opposed to proving a specific final dollar amount, but that would make it tougher to prove in court, he said.

In the July 25 call between Trump and Ukrainian President Volodymyr Zelensky, Trump asked Zelensky to help find information to attack the legitimacy of the investigation into Russian interference in the 2016 election, as well as damaging information about Biden. The White House on Sept. 25 released a document styled as a transcript of the call — it featured a warning that it wasn’t “verbatim,” though — that quoted Trump asking Zelensky for the “favor” of information after Zelensky pledged to buy more US military technology.

An as-yet-unidentified whistleblower filed a complaint about the call with the intelligence community’s inspector general, Michael Atkinson. Atkinson took the position that the Biden-related request could violate federal campaign finance laws, prompting a review by the Justice Department’s Criminal Division.

A senior Justice Department official, who spoke to reporters last week on condition of anonymity, said that members of the Criminal Division — including career prosecutors from the Public Integrity Section — who reviewed Trump’s call with Zelensky concluded that “whatever this was,” it lacked a “quantifiable value.” Without that, the official said, the department couldn’t formally open a criminal investigation.

The chair of the FEC, Ellen Weintraub, publicly criticized the Justice Department’s interpretation. On Sept. 26, the day after the White House released information about Trump’s call with Zelensky, Weintraub tweeted screenshots of a document she’d submitted to the commission outlining a proposed interpretation of the foreign contribution ban.

“On 'things of value' @FEC,” Weintraub wrote in the tweet, introducing the document. She then quoted from the text: “Indeed, the Commission has recognized the ‘broad scope’ of the foreign national contribution prohibition and found that even where the value of a good or service ‘may be nominal or difficult to ascertain,’ such contributions are nevertheless banned.”

An FEC spokesperson did not return an interview request for Weintraub on Thursday. The FEC currently lacks enough Senate-confirmed members to have a quorum, which means they cannot approve new investigations.

A Justice Department spokesperson did not return a request for comment.