It has taken a little more than six months for the U.S. national debt to grow by a trillion dollars, a quick clip that has little precedent over the nation's recent history.

Last week, the debt hit $21 trillion for the first time, rising from the $20 trillion mark it notched on Sept. 8. The debt is guaranteed to go higher, with President Donald Trump having signed a debt-limit suspension in February, allowing unlimited borrowing through March 1, 2019. Economists expect wider deficits to result from the tax cut Trump signed in December.

While a trillion-dollar increase over roughly six months isn't unprecedented — there was one in 2009, during the Great Recession, and another in 2010 — it's certainly fast.