MADISON - U.S. Sen. Ron Johnson said Sunday he doesn't trust the nation's intelligence agencies in a combative interview over allegations President Donald Trump withheld aid from Ukraine until government officials there launched an investigation into his political rival.

Johnson, chairman of the Senate's Homeland Security committee, said in an appearance on NBC's "Meet The Press" he hasn't trusted officials at the Central Intelligence Agency and Federal Bureau of Investigation since he was first elected nearly 10 years ago.

"No, I don't — absolutely not," Johnson told host Chuck Todd when asked whether he trusted the agencies. "No, and I didn't trust them back then."

Johnson said he didn't trust former officials including former FBI director James Comey and deputy director Andrew McCabe and former CIA director John Brennan.

Johnson appeared on the political talk show after revealing to reporters last week he was blocked by Trump from assuring Ukrainian officials U.S. aid was on its way amid allegations the president was withholding it until the eastern European nation investigated Democratic presidential candidate Joe Biden, the former vice president; and Biden's son.

Todd's interview with Johnson was heated from the start. Watch more here:

Full Johnson Interview: GOP attacks press over Trump's Ukraine actions

Johnson said Trump doesn't want to "dig up dirt" on Biden, but to determine whether Ukraine officials helped Hillary Clinton's campaign in 2016.

He said news reporters have misreported what the president wants from Ukraine out of bias — an accusation Todd said Johnson was using to avoid answering questions.

Also on Sunday, a new Fox News poll showed Trump was losing ground with rural voters in Wisconsin and was trailing his potential Democratic presidential opponents.

A poll of registered Wisconsin voters taken in the last week of September showed Biden leading Trump by 9 points, which is outside the poll's margin of error.

Vermont Sen. Bernie Sanders, who won the 2016 Wisconsin presidential primary, is preferred over Trump by 5 points and Massachusetts Sen. Elizabeth Warren has a 4-point lead over the president.

Undecided voters, however, could shift the race either way, the poll showed. Rural voters prefer Trump over Biden by 2 points, a group that voted for Trump over former Secretary of State Hillary Clinton in 2016 by 27 points.

RELATED:How Wisconsin's D.C. delegation has reacted to the Ukraine controversy and the House impeachment inquiry

Contact Molly Beck at molly.beck@jrn.com. Follow her on Twitter at @MollyBeck.