In a statement Sunday, Crapo took responsibility and pledged to ensure "this circumstance is never repeated."
"I am deeply sorry for the actions that resulted in this circumstance," said Crapo, 61. "I made a mistake for which I apologize to my family, my Idaho constituents and any others who have put their trust in me."
Word spread quickly that Crapo was arrested after authorities say he ran a red light and registered a 0.11 percent blood-alcohol level on a breath test in Alexandria, Va., where the legal limit is 0.08.
It took his colleagues in Idaho completely off-guard.
State Sen. Brent Hill of Rexburg said his son called him with the news Sunday, and his reaction was: "You must be talking about somebody else."
Hill is the Idaho Senate's top Republican, a position Crapo held while he was a state lawmaker from 1988 to 1992. Like Crapo, Hill is a Mormon.
"Obviously, I think many of us are very disappointed," Hill said. "As a citizen of the state of Idaho, we have a right to be disappointed, and as a member of his faith, I'm disappointed that a tenet of our faith didn't mean any more to him than evidently it did."
The state's junior U.S. senator, Republican Jim Risch, also was "very surprised" by the news, spokesman Brad Hoaglun said.
But Hoaglun said Crapo, a cancer survivor whose public image previously was squeaky clean, should be able to count on Idaho residents' forgiveness and understanding during what's clearly a difficult time.
"As a friend and colleague, I offer my support and help to him in any way I can," Risch said in a statement. "Senator Crapo has worked hard on behalf of Idahoans for many years and I have full confidence that Senator Crapo will continue his dedicated and unselfish service to the people of Idaho."
Risch is Catholic.
Idaho's two U.S. representatives, Raul Labrador and Mike Simpson, are Mormons, though Simpson has been open with constituents and media about drinking and smoking cigarettes. Neither Republican immediately responded to a request for comment.
Idaho politicians getting arrested for drunken driving is nothing new: Gov. C.L. "Butch" Otter was arrested in the early 1990s, when he was lieutenant governor; Democratic state Sen. Edgar Malepeai of Pocatello was arrested for DUI in 2009; and former state Sen. John McGee, a Caldwell Republican, was arrested on Father's Day 2011 after driving drunk and taking a car that didn't belong to him.
But none of them were Mormon.
By projecting an image as a diligent member of the faith, Crapo raised the stakes by at least outwardly following church founder Joseph Smith's 1833 revelation in which he advised members that "strong spirits are not for the belly."
The U.S. Senate adjourned last week and wasn't expected to resume until Wednesday; it's unclear why Crapo, who is married with five children, remained in Washington, D.C., ahead of the Christmas holiday.
According to the police report, he was alone in his car. It wasn't immediately clear where he'd been or where he was going.
Lindsay Nothern, a spokesman for the senator in Idaho, said Crapo would have no comment Monday. The lawmaker faces a court date Jan. 4.
Crapo was a Mormon bishop at 31 and has showed no public signs of a break from his church's teachings.
Church members must follow its guidance including its prohibition on alcohol to participate fully in the faith's rituals, including temple activities that are central to the religion.
Several phone calls Monday to LDS Church headquarters in Salt Lake City weren't immediately returned.
Crapo, first elected in 1998, is expected to take over the top Republican spot next year on the Senate Banking Committee. He also serves on the Senate's budget and finance panels and was a member of the so-called "Gang of Six" senators who worked in 2011 toward a deficit-reduction deal that was never adopted by Congress.
The 2010 bill he sponsored on cutting taxes for brewers ultimately stalled.