Past questions about a period when Democratic gubernatorial candidate Jared Polis paid no income taxes have resurfaced in a new TV ad that claims he was “caught” not paying taxes and sheltering his money in tax-free Cayman Islands accounts.

The Denver Post has previously reported that Polis owed no income taxes for five years in the early 2000s, before his election to Congress, while he was shouldering large losses as a tech startup entrepreneur. That means he had no tax bill due.

The Republican Governors Association-sponsored TV ad began airing Thursday, and Polis’ campaign began airing a TV ad Friday night disputing the charges, as well as hitting at his Republican opponent, state Treasurer Walker Stapleton.

A Polis campaign lawyer also sent letters to TV stations asking them to stop airing the RGA ad, asserting that it claims falsely that Polis violated the law.

“The ad intentionally, maliciously, and falsely communicates that Mr. Polis committed tax evasion,” said the letter, signed by Denver attorney Michael L. Bender.

The RGA ad is the sharpest elbow to be thrown so far in a race that’s expected to draw millions in outside spending this fall.

In announcing the ad last week, association spokesperson Jon Thompson argued that Polis’ history was relevant because Polis had failed to “pay his fair share in taxes” while advocating this year for a repeal of tax cuts championed by President Donald Trump.

The RGA ad includes snippets from a May 30 primary debate that was hosted by CBS4 reporter Shaun Boyd for Colorado Public Television. A question posed to Polis about his taxes — also juxtaposed with his tax cut repeal bill — relied on reporting that first came out during the 2008 Democratic primary campaign that would launch Polis to Congress.

Income tax returns provided back then by Polis to The Denver Post and the Boulder Daily Camera, covering seven years, showed that he paid no federal income taxes from 2001 through 2005.

In four of those years, his returns reported a net loss of income, according to the Daily Camera’s report. In the other years, however, the newspaper reported that Polis paid more than $18.4 million in income taxes on more than $120 million in adjusted gross income.

In short: When he paid no income taxes, it was because he didn’t owe any.

“In my business career, I only make significant money when I sell a company,” Polis told the Daily Camera in 2008, adding that his newer companies typically operated at a loss initially, as is typical for many startups.

During the May debate, this was Polis’ response to Boyd’s question: “Well first of all, I paid a heck of a lot of taxes in the years I made money. When you don’t make money, you can’t pay taxes, and since I’ve been in public service my expenses have been greater than my income, and that’s simply the fact, and I think that’s, you know, completely appropriate.”

The RGA ad, after quoting Boyd’s question about paying income taxes and having off-shore accounts, only includes the last part of Polis’ answer — that he believed his actions were “completely appropriate.”

The RGA ad’s claim about Polis having an offshore account is also an old charge based on his role as a managing partner for Jove Partners, a fund that had accounts both in the United States and in the Cayman Islands.

In 2008, the Rocky Mountain News reported that the Polis campaign said offshore accounts are commonly set up by such funds, in part, to attract foreign investment.

On Monday, Polis’ current campaign, in a written response to the RGA’s ad, said his money was only held in Jove’s U.S.-based account, for which he paid “all applicable taxes.”

“Jared Polis is the only candidate to release his tax returns for a 7-year-period and detailed financial holdings every year since being elected,” spokesperson Mara Sheldon wrote in an email. “Of course Jared has paid his federal income taxes and all taxes he has owed. No one has ever accused him of not paying taxes that were owed, which is why the false attack ad is so bizarre.”

The Post has requested more recent federal tax return filings from both the Polis and Stapleton campaigns. So far, neither has committed to providing them.