(CNN) Sen. Elizabeth Warren is slamming President Donald Trump's Federal Reserve pick Stephen Moore as "unqualified and unsuited" for the role.

In a stinging letter sent Friday , the Massachusetts Democrat and 2020 presidential candidate wrote that Moore has "a long history of making wildly inaccurate claims about economic policy that appear to serve political ends."

Moore, an economic commentator who advised Trump's 2016 campaign, has drawn controversy over his open criticism of recent Fed rate hikes, echoing Trump's own public attacks on the central bank -- a break from the tradition of presidents refraining from commenting on monetary policy moves.

Warren, in her letter, pointed out that Moore was quick to criticize low interest rates when Barack Obama was president, but that he has since reversed that position as Trump has turned on the Fed's efforts to keep the economy in check as it absorbs the Republican tax cut and other expansionary measures backed by the President.

She also specifically called out Moore's role in developing former Kansas Republican Gov. Sam Brownback's tax cuts, which triggered a budget crisis and which were ultimately reversed by Republican lawmakers

Moore did not immediately respond to a message left for comment on Warren's letter.

He has repeatedly defended himself against accusations that he's unqualified for the role, asserting in a CNN interview on Thursday that the central bank can be "divorced from politics."

"I have 35 years experience in the policy game. I was the youngest budget analyst in Washington at the age of 25. I was, served as Donald Trump's economic adviser. I'm very proud of what we accomplished. A lot of people said it would be impossible to make this agenda work," Moore told CNN's Erin Burnett on "OutFront."

"I think my qualifications stand up pretty well," he said.

Moore also said he would not be the first member of the board with close ties to a sitting president, referencing former Chairman Ben Bernanke, who served as chief economist to President George W. Bush.

"I do believe in the importance of an independent Fed," said Moore, a former CNN analyst. "I think it can be divorced from politics."

He added: "It's not unusual for the president to take someone who agrees with a lot of his economic views."

Warren's letter comes as Republican senators have turned on Trump's other Fed pick, former Republican presidential candidate Herman Cain, whose candidacy was effectively ended in 2011 by allegations of sexual misconduct. Cain has steadfastly denied those allegations and this past weekend posted a video to Facebook again vowing to fight them

Four Republican senators said this week that they would vote no if he is nominated , leaving him no clear path to confirmation.

Warren wrote a separate letter to Cain Friday, claiming he's had shifting views on monetary policy and raising concern about his pro-Trump super PAC.

"You have made comments regarding Federal Reserve policy that suggest an alarming lack of understanding of important aspects of the Federal Reserve's role and monetary policy," she wrote.

Republicans have been warmer to Moore, though he also faces personal issues, including a tax lien of more than $75,000.

"The distinction's pretty clear. I know him. I know his philosophy, I know his economic positions, I know his credentials, I know his heart, and I think he'd be a good addition to the Fed. The issues that have been raised about Stephen, none of them disqualify him," North Dakota Republican Sen. Kevin Cramer told CNN of Moore on Thursday. "Those are sort of issues of life. Sexual harassment is quite different."