Mick Mulvaney is Donald Trump's pick to lead the Office of Management and Budget

President-elect Donald Trump nominated Rep. Mick Mulvaney (R-S.C.) to lead the Office of Management and Budget, a key administration role that not only helps craft the president's budget proposals, but also calculates how much his policies would cost if enacted.

"Right now we are nearly $20 trillion in debt, but Mick is a very high-energy leader with deep convictions for how to responsibly manage our nation's finances and save our country from drowning in red ink," Trump said in a news release announcing Mulvaney's nomination. "With Mick at the head of OMB, my administration is going to make smart choices about America's budget, bring new accountability to our federal government, and renew the American taxpayer's trust in how their money is spent."

Mulvaney is one of the most conservative members of the House, helping found the House Freedom Caucus, a group of rabble-rousing Republicans who have been a thorn in the side of House leadership.

A member of the tea party, Mulvaney is a hard-liner when it comes to spending, unafraid to shut down the government over spending deals. 

He's also against raising the debt ceiling. 

If the debt ceiling, the maximum amount the government is allowed to borrow, is not raised, the United States would default, making it unable to pay its bills and potentially causing a financial crisis.