KUSA-- Republican frontrunner Walker Stapleton has been running a false ad in his campaign for governor for weeks now—and he’s still running it.

His opponents are accusing him of “lying.”

That’s a strong word. Is it fair to use?

The falsehood from Stapleton took on a life of its own in the GOP primary to the point where one of his opponents, Vic Mitchell, cut an attack ad about it.

CLAIM: “Political insider Walker Stapleton got caught lying about his own record.”

VERDICT: TRUE

We rate this attack true, and we don't take a word like "lying" lightly. It implies a willful intent to deceive you, which is a hard thing to prove.

And yet Stapleton started running his false ad roughly a month ago and he's still running it.

In that ad, Stapleton claimed in his own voice: “I was the only Treasurer in the country with the courage to support Donald Trump's tax cuts.”

We rated that claim false in a Truth Test last month. It’s easily disproved because several other GOP state treasurers publicly supported the President’s plan.

We don't know what Stapleton was thinking when he started running this ad, but we know he knows better now.

In the 9NEWS Republican debate Thursday night, Stapleton acknowledged that what his ad says isn't true.

What’s more, he said it's not important that it isn't true:

9NEWS: I'm asking you about whether you've learned anything about being caught making a false claim?

STAPLETON: No. No. I actually have not. Because I don't think the semantics of being "one of or the first" or "the first" are really meaningful.

Not only is Stapleton saying the truth of the matter isn't meaningful, but he gave a misleading answer that re-writes his own history in the above exchange.

His ad didn't claim he was the "first" treasurer to support President Trump's tax plan. He said he's the “only” one who supported it.

Even if it was about being first, other State Treasurers physically went to the White House to support the president's tax plan the month before Stapleton gave it his support in a White House press release.

BOTTOM LINE: Stapleton's been making this false claim for weeks now.

He's been thoroughly debunked. He knows his ad is false. And yet he's still running it.

We should note that FCC regulations ban TV stations from rejecting candidate ads. “Legally qualified candidates” have the right to “use” of the public's airwaves, regardless of what they put in their ads.

We can't take his ad down, but it's fair for his opponents to call it a lie.

If Mr. Stapleton doesn't want to be called a liar, then he should stop saying something he knows is false.