President Donald Trump spent the weekend publicly bashing special counsel Robert Mueller’s investigation, raising new fears that the president might take the extreme step of actually firing Mueller in an attempt to end the probe.

But even if the Mueller investigation survives, the public may never get to hear most of what he ultimately finds.

That’s because Mueller is only required by law to deliver a confidential report to Deputy Attorney General Rod Rosenstein, who oversees the investigation. And Rosenstein has no obligation to send the report to Congress or tell the public about it. Which means much of what Mueller uncovers may remain a secret.

Now, Rosenstein could choose to make some or all of the report public, but he’s only required to notify Congress if Mueller proposes some action that is “so inappropriate or unwarranted” under Justice Department rules “that it should not be pursued.” So unless Mueller does something Rosenstein finds objectionable, he can keep the report secret.

Mueller certainly knows this, which is why he’s using his indictments to reveal part of what he’s finding. “He is telling a story through the indictments that he files in court, which are painting a vivid picture of Russian efforts to interfere in the election,” Jens David Ohlin, the vice dean of Cornell Law School, told me.

And because of the way the special counsel is set up, that picture may end up being the closest thing the public ever gets to a full accounting of what happened between the Trump campaign and Russia.

Why Mueller can’t just tell the public what happened

There’s an additional problem beyond what happens to Mueller’s final report. Most of Mueller’s work is through a grand jury, a special panel put together to hear evidence and issue subpoenas and other court orders. And there are strict laws prohibiting the release of information about a grand jury’s work.

In addition, a lot of what Mueller has been sorting through deals with intelligence and classified materials.

With all those restrictions, the real decision on what to do will be left up to Rosenstein. Rosenstein has the option to release material if he thinks it’s in the public interest, according to the special counsel law.

But Mueller can try to make Rosenstein’s decision on whether to release the report a little easier. When Mueller has wrapped up his investigation, he’s likely to give Rosenstein both his legally obligated report and a scrubbed summary that could be released to the public.

“The first would be the ‘full report’ which includes classified materials and confidential grand jury transcripts,” Ohlin said. “The second report would be an ‘executive summary’ (but still thousands of pages) that excludes confidential and classified material and is ready for public release by Rosenstein if he so chooses.”

But with Trump’s team already pushing Rosenstein to kill the investigation altogether, Rosenstein will likely see enormous pressure to keep the report secret. And Victoria Nourse, a law professor at Georgetown, told me that Trump even has the to power to force Rosenstein’s hand.

“The president can order him not to release it,” Nourse said. “But that’s a bit like firing Mueller, as many Republicans have warned — it just ups the case for impeachment because the president appears to be hiding something.”

Mueller’s one public outlet is the indictments he has filed, which have provided proof of Russian efforts to meddle in the 2016 presidential election despite frequent White House denials. But beyond the indictments, he can’t talk about what he finds.

Without any kind of public report, the full scale of what happened during the election may never be known. If Bill Clinton’s impeachment is any prologue, any action against Trump is also highly unlikely unless Mueller finds something and tells Congress, and Democrats win back the House.

Elections, not Mueller’s report, will decide impeachment

The last time an independent counsel went digging for potential crimes by a president, the investigation produced a 211-page public report about Bill Clinton’s presidency that would become a New York Times best-seller. Independent counsel Ken Starr’s four-year investigation — and the salacious details of Clinton’s affairs Starr revealed in his final report — ultimately led to Clinton’s impeachment.

But while Starr was required by law to give Congress his findings, Mueller isn’t. That’s because Starr was working under an older law that expired in 1999, the Ethics in Government Act, while Mueller is constrained by Justice Department regulations. That means that while Starr could independently dictate the impeachment story, Mueller has bosses.

When Clinton was impeached, he faced a Republican House eager to encourage his removal. Led by Speaker Newt Gingrich, Republicans filed articles of impeachment based solely on the details obtained by Starr.

This time Trump has a friendly Congress that is unlikely to turn on him the same way. That could change as a result of the midterm elections, with Democrats looking increasingly likely to take the House.

Impeachment is a political decision, not a legal one. “While it looks and feels a whole lot like a legal or judicial process, in practice impeachment is dominated by politics from start to finish,” Vox’s Andrew Prokop wrote in December. “That’s because, rather than being run by any courts, impeachment and any ensuing presidential trial are carried out by the House of Representatives and the Senate, which are partisan bodies.”

With the House investigation closed, Mueller will be the chief source of information that could help trigger impeachment proceedings. While a Senate investigation also continues, it’s the House that would need to trigger the impeachment process.

But because impeachment is political, whether the full details come out may not matter.

“If Dems take the House, they can convene an impeachment committee and use what they have from the old intel hearings, Senate, Mueller trials, etc.,” Nourse, the Georgetown professor, said. “They don’t need a report. The question is whether there is a political will to impeach.”