GEOFF BENNETT: With Donald Trump and in Miami courtroom today, the first ex-president ever indicted on federal criminal charges, the chorus of his Republican supporters asking the question "But what about the Democrats?"

has grown even louder.

Laura Barron-Lopez reports on why the DOJ charged Mr. Trump for his handling of classified material, but not others, like Hillary Clinton, Joe Biden, and Mike Pence.

REP. JIM JORDAN (R-OH): This is the most political thing I have ever seen.

LAURA BARRON-LOPEZ: In response to the unprecedented federal indictment of Donald Trump... GOV.

RON DESANTIS (R-FL), Presidential Candidate: Is there a different standard for a Democrat secretary of state versus a former Republican president?

I think there needs to be one standard of justice in this country.

LAURA BARRON-LOPEZ: Republicans, including the former president, are attacking the justice system.

DONALD TRUMP, Former President of the United States: The ridiculous and baseless indictment of me by the Biden administration's weaponized department of injustice will go down as among the most horrific abuses of power in the history of our country.

JACK SMITH, Special Counsel: An indictment was unsealed.

LAURA BARRON-LOPEZ: The Justice Department charged Trump with 37 felonies, including 31 counts under the Espionage Act, for knowingly retaining national defense documents after repeatedly being asked to hand them over.

REP. NANCY MACE (R-SC): Joe Biden has classified documents.

He mishandled them as vice president.

LAURA BARRON-LOPEZ: Republicans are crying hypocrisy, and GOP primary voters agree.

Three-quarters say the prosecution is politically motivated, according to a recent CBS News poll.

MAN: It's a witch-hunt.

WOMAN: I think it's a complete waste of time.

DONALD TRUMP: They did absolutely nothing in Hillary's case.

LAURA BARRON-LOPEZ: Trump and his allies are pointing to other cases where classified material was found in the possession of former government officials, but not prosecuted, in particular, Trump's 2016 rival, Hillary Clinton.

HILLARY RODHAM CLINTON, Former U.S. Secretary of State: I did not send nor receive classified material.

LAURA BARRON-LOPEZ: Some 30,000 e-mails from Clinton's years as secretary of state, including some deemed classified, were found in a personal e-mail server in her New York home during the 2016 campaign.

Clinton cooperated with an FBI investigation, which recommended no criminal charges.

JAMES COMEY, Former FBI Director: Although we did not find clear evidence that Secretary Clinton or her colleagues intended to violate laws governing the handling of classified information, there is evidence that they were extremely careless.

MARK ZAID, National Security Attorney: Hillary Clinton's case is completely different.

LAURA BARRON-LOPEZ: Mark Zaid is an attorney who focuses on national security issues.

He says Trump and Clinton were investigated under two different Espionage Act provisions.

And Clinton was dealing with e-mails, not marked classified document.

MARK ZAID: But most of the information that was deemed to be classified was actually deemed based on the content after people reviewed it, so that those who saw it wouldn't necessarily have suspected there was anything classified in it.

LAURA BARRON-LOPEZ: As for the investigations into President Biden and Trump's own vice president, Mike Pence, there are key differences.

In Trump's case, the DOJ charged him for holding onto classified materials for more than a year after leaving office, documents he stored in places like a bathroom and ballroom.

Both Biden and Pence found classified material from their time as V.P.

in their homes.

But, unlike Trump, both turn them over immediately, and invited the FBI to search for others.

DAVID KELLEY, Former U.S. Attorney, Southern District of New York: When you talk about President Biden and former Vice President Pence, what you're talking about is complete transparency.

LAURA BARRON-LOPEZ: David Kelley is a former U.S. attorney of the Southern District of New York.

DAVID KELLEY: You screwed up.

You weren't supposed to take these documents.

Then you gave them back.

We're good.

But when you go ahead and you're told that you have got documents you're not supposed to have, and then you conceal that, and then you lie about it, that's a criminal problem, because that shows knowledge and intent to violate the law.

LAURA BARRON-LOPEZ: The DOJ recently cleared Pence, and a special counsel investigation of Biden is ongoing.

The Trump indictment alleges that he conspired to hide documents from the government, returning them only after a subpoena and a later FBI search.

Dozens of other classified documents he had taken to Florida, but turned over to the National Archives earlier, were not included in the charges.

DAVID KELLEY: The compounding factor in the Trump indictment is the obstruction of justice.

He was told he had documents.

He kept them anyway and then took steps to keep them from the National Archives.

LAURA BARRON-LOPEZ: While Trump had hundreds of classified documents stored in Florida, the special counsel narrowed its case to just 31 pages.

That includes 21 with -- quote -- "top secret markings" from the CIA, NSA, the Pentagon and Department of Energy,among others.

According to the indictment, the documents contain secrets about U.S. nuclear and military capabilities and defense capabilities of foreign countries.

MARK ZAID: Some have said the Goldilocks documents.

LAURA BARRON-LOPEZ: Mark Zaid says these 31 documents were chosen carefully by the special counsel.

MARK ZAID: It's not too secret, and it's not too challengeable, meaning these are documents that probably anyone who looks at them would understand, as a layperson, that the information is incredibly sensitive.

LAURA BARRON-LOPEZ: It will soon be up to a Florida jury to decide if Trump will face criminal consequences.

For the "PBS NewsHour," I'm Laura Barron-Lopez.