The economic plan of GOP presidential front-runner Donald Trump is "especially troubling," anti-debt crusaders Erskine Bowles and Alan Simpson told CNBC on Friday.
Eliminating the federal debt without touching entitlements, as Trump has promised, would be impossible, said Bowles, the Democratic co-chair of President Barack Obama's 2010 bipartisan debt commission.
"The arithmetic just won't work," Bowles said in a "Squawk Box" interview. He said a combination of economic growth, tax increases and spending cuts are needed to get the job done.
In an interview this month with The Washington Post, Trump said he would be able to eliminate the $19 trillion national debt "over a period of eight years."
Trump said "renegotiating all of our deals" would supercharge economic growth and enable the U.S. to pay down the debt.
The Obama debt commission's Republican co-chair, former Wyoming Sen. Simpson, said it's "fantasy" to believe it's possible that increased economic growth alone can wipe out the deficit.
"You could get up to 10 percent [growth] and it would take you 20 years to dig out of this hole," Simpson said on "Squawk Box," sitting next to Bowles.
The 2010 Bowles-Simpson plan fell short of the votes from the bipartisan panel needed to recommend the framework to Congress.
Simpson was also highly critical of Trump, as well as GOP presidential hopeful Texas Sen. Ted Cruz.
Describing the current state of the Republican race, Simpson said: "It's madness."
"It's going to be a very disruptive, disemboweling thing of the Republican Party," he said.