Sen. Bernie Sanders, the Vermont independent who is seeking the Democratic presidential nomination, for years has drawn a pension for his eight-year stint in the 1980s as mayor of Burlington even has he received a salary as a member of Congress.
Sanders, who earns $174,000 as a senator, received $5,241 from Burlington's pension system in 2018, according to his federal income tax return.
His total income with his wife, Jane O'Meara Sanders, that year was $561,293, which was down from the more than $1 million they earned in the prior two years, largely as a result of his book about running for president in 2016.
Public financial disclosure records show that Sanders, who began serving in the U.S. House of Representatives in 1991 and in the Senate in 2007, has received nearly $62,000 in Burlington pension payouts since 2005.
That practice, known as "double-dipping," isn't illegal.
Nor is it unknown in Congress, where a National Journal study in 2013 found that nearly 20% of members have drawn government pensions while serving in the Senate or the House, for a total haul of more than $3.6 million in such pensions in the prior year.
But double-dipping does rub some public watchdogs — and even elected officials — the wrong way.
In fact, in 2014, former Obama administration official Ro Khanna, while conducting a challenge to incumbent Rep. Mike Honda of California, blasted his fellow Democrat Honda for double dipping. Honda at the time was receiving three pensions related to government jobs, including one belonging to his late schoolteacher wife.
"Those pension benefits are supposed to support public workers in their retirements — not while they're still serving and collecting a salary of $174,000 a year," Khanna said in 2014.
Khanna lost his challenge to Honda in 2014, but defeated him in 2016 – the same year that Khanna endorsed Sanders' first run for president.
And in February, Khanna joined Sanders' second bid for the White House, serving as one of four national co-chairs of Sanders' campaign.
Khanna's congressional office referred CNBC's questions about his current view of double-dipping on public pensions to the Sanders campaign.
David Sirota, a senior aide to Sanders, told CNBC when asked for comment, "Like other past Burlington mayors, Senator Sanders receives a municipal pension for his service as mayor of Burlington."
Sanders has been an advocate in Congress for protecting workers' pensions. In 2017, he co-sponsored legislation, the "Keep Our Pension Promises Act," with Rep. Marcy Kaptur, D-Ohio, to "reverse a provision passed in 2014 that could result in deep pension cuts for millions of retirees and workers in multi-employer pension plans," according to Sanders' Senate web site.
Steve Ellis, executive vice president of the non-profit federal budget watchdog group Taxpayers for Common Sense, when asked about Sanders' pension, said: "Yeah, it's technically legal."
"There's no rule against it, or whatever. That doesn't make it right," Ellis said. "He's being paid by taxpayers at two different levels."
"He's being paid $174,000 as a U.S. senator. He's not retired," Ellis said. "In reality, pensions are to be paid when you retire."
Ellis noted that Sanders is unlike most Americans, who are not eligible for a pension, much less for one when they are employed in another job full-time.
Ellis said that some states ban double-dipping, and that others should. And, he added, even if Sanders is technically eligible to receive a pension, he should "make a contribution to charity or return it to the city of Burlington" while he's still working.
"Once he retires, that's a different matter," Ellis said.
"The optics of it aren't very good," Ellis said. "Just from a political standpoint. Why take the heat over five grand?"
When told about Khanna's past criticism of double dipping and his current role as a top advisor to Sanders' campaign, Ellis laughed and said, "Well, I think he was right" in 2014.
"It would be worth him talking to Sen. Sanders and saying, 'This is not a lot of money and this is not a good look."
But Art Woolf, an associate professor of economics at the University of Vermont, said that not only is what Sanders doing "perfectly legal," it makes good economic sense.
"As an economist, I'd say if the government has a rule or regulation and these are the requirements to get a pension and you fit those requirements, you get it," said Woolf, who added that he is "no Bernie Sanders supporter."
Woolf added, referring to Sanders' annual pension, that "$5,000 seems to me a pretty small amount ... and pretty low for working for a city, given someone who worked for eight years" as mayor.
One counter-example to Sanders and others in Congress who receive a public pension is former Rep. Chris Gibson, a Republican who represented an upstate New York district from 2011 through 2017.
A U.S. Army veteran who served in the first Gulf War, Kosovo and Iraq, Gibson retired as a colonel in 2010 after 24 years of service. During his tenure in Congress he returned his military pension, which totaled $4,300 per month, to the government.