And at his stops in Michigan yesterday, Rick Santorum spoke of economic revival through low taxes, fewer regulations and his commitment to conservative family values.
Here's NPR national political correspondent Don Gonyea.
DON GONYEA, BYLINE: Rick Santorum can't outspend Romney in Michigan, and he's facing a barrage of ads on radio and TV paid for by the pro-Romney superPAC Restore Our Future. The ads attack Santorum's U.S. Senate record.
Symbolically speaking, this month's Michigan's primary may be the most important of the GOP presidential race to date. It's the state where Mitt Romney grew up, and his father was a beloved government and business leader. And now, Romney seems to have a real chance of losing the state to Rick Santorum.
This week the state of Nevada finalized new rules that will make it possible for robotic self-driving cars to receive their own special driving permits. It's not quite driver's licenses for robots — but it's close.
The other day I went for a spin in a robotic car. This car has an $80,000 cone-shaped laser mounted on its roof. There are radars on the front, back and sides. Detailed maps help it navigate.
Do people notice it's a self-driving car and gawk?
A closed-door meeting to discuss controversial bird flu research is drawing to a close at the World Health Organization in Geneva, and the WHO plans to publicly report on what happened once it's officially over.
Bill Burton, shown during a news briefing at the White House in January, is now with pro-Obama superPAC Priorities USA Action. He says the superPAC is "careful to make sure that we are in compliance with the rules."
Jiang Shixue is describing to me one of the most exciting moments of his life: The moment earlier this month when one of the most important people in Europe — German Chancellor Angela Merkel — came to visit his workplace.
"She said that the EU would be happy to see if China can offer a kind of helping hand," says Jiang, an academic at the Chinese Academy of Social Sciences.
The Lucky Friday Mine in Idaho's Silver Valley, shown in 2007, was temporarily shut down in January while it complies with safety regulations, according to the mine's operator, Hecla Mining.
Credit Nick Geranios / AP
The recent spike in metal prices, combined with a shortage of miners, means mining companies are hiring. So some teens are opting not to go to college, and instead are heading underground. A miner is shown at work in Newmont Mining's Leeville mine near Carlin, Nev.
Henry Flores was walking down the hallway at St. Mary's University in San Antonio when he noticed that the last office in the hallway's door was open.
"I just kind of looked inside to see who was in there, and I saw a flash of ankle, and I saw this blond hair, and I went smack-dab into the wall," says Flores, who is now a professor of political science and dean of the graduate school at St. Mary's.
It was the mid-1980s and Gwendolyn Diaz, who had just joined the university faculty, was sitting in the office.