David Welna, NPR

Critics in the Senate have posed a high-stakes question: Can anything keep President Trump from launching a nuclear attack on his own?

"We are concerned that the president of the United States is so unstable, is so volatile, has a decision-making process that is so quixotic that he might order a nuclear weapons strike that is wildly out of step with U.S. national security interests," said Connecticut Democrat Chris Murphy.

His Massachusetts colleague Ed Markey has offered legislation that would require congressional approval for any first use of nuclear weapons.

This week saw both a frantic finale to the much-unloved 112th Congress and, hours later, the swearing in of the new 113th. The cast of lawmakers and their leaders is mostly unchanged. The same can be said for Capitol Hill's never-ending drama over taxes, deficits and spending.

What was arguably this week's most sensational congressional moment did not even take place in Washington. On Wednesday in Trenton, N.J., Republican Gov. Chris Christie blasted the GOP-led House for closing down the last Congress without even considering a Superstorm Sandy disaster relief bill.

The U.S. Senate wrapped up a tumultuous year of divided government with votes that keep the federal government funded through September and extend expiring unemployment benefits and a payroll tax cut another two months.

In a rare Saturday year-end session, the Senate's action averted a shutdown but was not the last word on the payroll tax cut extension.