About a year after President Trump took office, the White House quietly began storing text messages sent and received by aides on work phones, establishing a repository of potential evidence that Democrats could search in their impeachment investigation.

It’s unclear if Democrats will seek to acquire the texts before voting to make Trump the third president ever impeached. But if they do, the messages may contain missing evidence proving Trump tied foreign aid to Ukraine investigating Democrats. They also could exonerate him.

The White House began collecting text messages from service provider Verizon in early 2018 after overcoming technical hurdles dating to the Obama administration, multiple sources involved in technical and legal discussions told the Washington Examiner.

The messages will be released to the public as early as five years after Trump leaves office under the Presidential Records Act unless Democrats force earlier release.

Sources said they believe the White House does not store call detail records for official cellphones, heightening the potential value of text messages.

“There is little doubt that White House text messages could be of tremendous value in the current impeachment inquiry,” said Steven Aftergood, who directs the Project on Government Secrecy at the Federation of American Scientists. “We have already seen the value of text messages from State Department officials, among others, during the most recent hearings.”

Trump does not text, but several senior aides use unencrypted SMS messages to communicate with reporters and other officials, making the messages subject to acquisition and storage.

Although emails also are archived, one source said White House staff are wary about using email to transmit potentially incriminating information. “Most of the bad actors over there think email is only evidence, and phones are the only safe bet,” the source said. He requested anonymity due to the sensitivity of discussing White House procedures, saying: "I don’t want to get an invitation to Capitol Hill."

“The White House having them and Congress getting them are different things,” said one former White House official with direct knowledge of the text message retention.

Before automatic text-retention began, there was an honor system during Trump’s first year in office. White House staff phones weren’t able to send texts, and when an official sent work messages on personal phones, they were supposed to screenshot the messages and email them to themselves, so they could be archived via staff email. Now, all messages are captured by Verizon and sent regularly to White House technology staff.

Personal cellphones are banned in West Wing spaces. The policy is sporadically enforced, and some officials still use them, loaded with encrypted texting apps such as Signal or WhatsApp to avoid interception. Official cellphones cannot use these apps.

To date, evidence has been incomplete that Trump withheld more than $400 million in foreign aid to Ukraine as part of a quid pro quo to force Ukraine to investigate Democrats. Senior White House aides have refused to testify or provide documents, though a court fight featuring former White House counsel Don McGahn could open the door to compelling testimony or evidence. A ruling is expected by Monday in the McGahn case, though that could be appealed.

Some of the strongest evidence acquired by the House Intelligence Committee has been text messages. Former special representative to Ukraine Kurt Volker shared messages he traded with acting U.S. Ambassador to Ukraine Bill Taylor, U.S. Ambassador to the European Union Gordon Sondland, and Ukrainian official Andriy Yermak. But the messages are not decisive, appearing to hint at a quid pro quo despite Sondland writing that Trump was “crystal clear: no quid pro quo’s of any kind.”

In one message, Sondland writes, “I think potus really wants the deliverable,” appearing to establish the link. But Sondland testified last week that he only presumed Trump’s intentions and that Trump directed him to “speak with Rudy [Giuliani],” Trump’s personal lawyer, who urged pressure on Ukraine.

Weak evidence could result in party-line votes that impeach Trump but fail to remove him from office in the Republican-held Senate. Texas Rep. Will Hurd, a Republican seen as a possible vote against Trump, said last week that he opposed impeachment due to a lack of “overwhelmingly clear and unambiguous” evidence. He said the process was “rushed.”

“The more evidence you can have the better. The evidence could be exculpatory,” said attorney Michael Conway, the counsel for the House Judiciary Committee when it voted in 1974 to impeach Richard Nixon.

The Watergate scandal unfolded more slowly than the impeachment case against Trump. The 1972 Democratic office burglary was followed in 1973 by a special Senate committee that investigated the subsequent White House cover-up. A special prosecutor fought successfully to release tapes Nixon made in the Oval Office, which proved he ordered a cover-up, causing Republican allies to abandon him and leading to his resignation.

“We didn’t have to start from scratch investigating,” Conway said.

“Under the circumstances, the House impeachment inquiry has proceeded remarkably quickly from the whistleblower complaint to the public hearings,” Aftergood said.