WASHINGTON — Pursuing a return to public service came at a cost to Bill and Hillary Clinton, as their considerable joint income dropped by nearly two-thirds last year when the former secretary of state began her run for president.

The Clintons released their most recent tax filing Friday, as well as 10 years of tax documents from running mate Tim Kaine and his wife, part of a renewed call on Republican nominee Donald Trump to do the same.

For more than a year, Republicans and Democrats have pushed the real-estate magnate to back up his boasts about business acumen and charitable giving by disclosing federal and state tax filings, a customary gesture of transparency for presidential aspirants and one his rivals were confident could offer political ammunition.

“Donald Trump is hiding behind fake excuses and backtracking on his previous promises to release his tax returns,” Clinton campaign spokeswoman Jennifer Palmieri said in a statement.

But Clinton's gesture was not without risk. It invited a fresh look at the sources of income for she and her husband that have spawned political attacks before.

Hillary Clinton, who announced her candidacy in April 2015, earned $1.48 million from speaking engagements in 2015, a sharp decrease from the nearly $10.5 million she generated the year before.

Her husband earned $5.25 million in speaking fees in 2015, less than half the previous year.

The couple also generated additional income from book sales and Bill Clinton's consulting business. Both listed the same occupation on returns signed in March: “speaking and writing.”

Together they reported an adjusted gross income of $10.6 million in 2015, down from nearly $28 million the year before. Their combined payments in federal, state and local taxes amounted to an effective tax rate of 43.2 percent, the sixth time in 15 years it exceeded 40 percent.

By comparison, the Kaines' joint adjusted gross income was a far more modest $313,441, reflecting the vice presidential nominee's income as a U.S. senator and his wife's as Virginia secretary of education.

The average payout for a single Clinton speaking engagement exceeded the $174,000 annual Senate salary of her running mate.

The Clintons made a combined $153 million from 729 paid speeches from 2001 to May of 2015, a CNN analysis found this year. With the latest release, the Clintons have disclosed nearly four decades of tax returns, dating to Bill Clinton's first year as attorney general of Arkansas.

The Trump campaign charged that Clinton has “turned over only the records nobody wants to see from her.” Instead of tax documents, Americans want to see the 33,000 emails deleted from Clinton's private server, transcripts of her paid speeches to firms with Wall Street ties and other documents from the Clinton Foundation, Trump spokesman Jason Miller said in a statement.

“Hillary Clinton is at the center of an international corruption scandal that reveals her use of government authority and influence for personal gain,” Miller said. His statement did not address Trump's tax returns.

Candidates' disclosure, or lack thereof, of tax returns has been a staple of presidential campaigns.

In 2012, the top Senate Democrat, Harry Reid of Nevada, helped build pressure on Republican nominee Mitt Romney to release his returns by suggesting he had paid no taxes at all.

Romney eventually released a single year's filing and a summary of taxes paid for two decades.

This year, while not a candidate himself, Romney demanded that Trump provide similar disclosure as part of an ultimately unsuccessful campaign to discredit the GOP front-runner during the primaries.

Romney's comments — saying the disclosure would show whether Trump was a “real deal or a phony” — were included in an online video produced by the Clinton campaign Friday that also included similar attacks from his GOP rivals.

Trump has said he could not release his tax returns because they were under audit by the Internal Revenue Service, an explanation he repeated Thursday in an interview on Fox News.

“You don't learn very much,” he said. “I have been under audit now for, I think, 15 years straight, which is ridiculous because other people don't get audited.”

No law or rule prevents Trump from releasing tax information while under audit, according to the IRS, though tax experts have cautioned against releasing information from the years under audit.

michael.memoli@latimes.com