The OIRA also meets with and considers the input from industry stakeholders impacted by proposed rules.

Mulvaney was elected to the House of Representatives in 2010 as part of the Tea Party Movement, and has developed a reputation as a fiscal hawk.

After winning a Congressional seat that had been held by a Democrat since 1883, Mulvaney went on to be a founding member of the House Freedom Caucus, which is comprised of roughly 35 of the House's most conservative members.

Mum on fiduciary rule, but plenty to say on Social Security

This week, Mulvaney faced hours of questioning from two Senate confirmation pannels–the Budget Committee and the Homeland Security and Governmental Affairs Committee.

He did not field questions on Labor's fiduciary rule, as neither subcommittee has jurisdiction of Labor or retirement issues.

But he was pressed for his opinions on Social Security reform from Republican and Democrat senators, and how he would advise President Trump on the issue.

During the Budget Committee hearing, ranking member Sen. Bernie Sanders, I-VT, noted Trump's repeated campaign commitments to not cut Social Security.

Sanders also claimed Mulvaney's views on Social Security throughout his political career have been "exactly opposite" of Trump's campaign pledges.

Mulvaney has advocated for immediate reforms to assure the solvency of Social Security, and last year voted against a Republican budget proposal because it did not aggressively enough address funding shortfalls of Social Security and other entitlement programs.

"It does not make sense to me to have a key advisor to the President that holds views directly in opposition to what the President campaigned on," said Sanders in his opening remarks.

Sanders asked Mulvaney what he would tell President Trump regarding his campaign pledges to not reform Social Security.

"The only thing I know to do is to tell the President the truth," said Mulvaney.

Sen. Bob Corker, R-TN, said President Trump's campaign positions on Social Security and entitlement reform were "unrealistic" and "make no sense whatsoever."

Sen. Lindsay Graham, R-SC, asked Mulvaney if he would tell President Trump that his campaign promises will lead to the demise of Social Security and Medicare.

"Yes sir," said Mulvaney.

"Will you tell him there is bipartisan way to do this without gutting the program that saves the program," asked Graham.

"I am familiar with those proposals, yes sir," said Mulvaney, who agreed to a phased increase in the retirement age and means testing as ways to address Social Security's funding shortfall.

Mulvaney was less supportive to raising taxes on the wealthy to address retirement shortfalls, saying the government could "confiscate" everything the 1 percent wealthiest of taxpayers has and still not close the entitlement funding shortfalls.

He also said growing the economy, even at 8 percent, would fail to adequately fund the shortfalls.

On the campaign trail, Trump said his economic policies and the growth they would spur would suffice in raising the revenue to maintain Social Security's solvency.

In a statement, Maya MacGuineas, president of the non-partisan Committee for a Responsible Federal Budget, said, "Rep. Mulvaney's testimony demonstrated a willingness to speak hard truths on the need to make changes to Social Security and Medicare, which represent the largest and fastest growing parts of the budget and are both on paths toward insolvency."

She added: "It is encouraging that Rep. Mulvaney bucked the increasingly common trend of pledging not to touch these programs or the revenue sources needed to pay for them. These pledges virtually guarantee the country remains on an unstainable fiscal course and will ultimately hurt the people who rely on these programs most."