NEW YORK —  That mushroom cloud you see in New Mexico isn't a new round of atomic bomb tests. It's former Clinton Energy Secretary Bill Richardson storming toward the statehouse — and turning this once Republican-led state into a Democratic outpost in the Southwest.

Richardson defeated freshman Republican state Rep. John Sanchez 58 to 36, with 80 percent of precincts reporting.

Republican Gov. Gary E. Johnson was forced to step down after being term-limited, so the GOP chose Sanchez, a businessman still in his first term in the House.

Before delivering a concession speech, Sanchez telephoned Richardson and congratulated the Democrat on his win.

"I always said that the next governor of the state of New Mexico would have a mandate when it came to lowering taxes and reforming our tax system here in the state," Sanchez told supporters. "You know what, Mr. Richardson, we stand with you today. Let's lower taxes in New Mexico."

Young, energetic and successful, Sanchez was seen as an up-and-comer when he surged onto the political scene in 2000. But a bitter Republican primary against Lt. Gov. Walter Bradley sapped some of the enthusiasm of the state party for him.

Richardson, on the other hand, stepped into his campaign boots well-respected within his party, brandishing an impressive resume — including U.N. ambassador and 15 years as congressman — and backed by much of the state's business community.

Those credentials are what led Sanchez to call him a "career bureaucrat," and Richardson was still vulnerable to attacks regarding the Energy Department scandals that fell over the state while he was in charge. But Sanchez's moves weren't enough to win him the governorship.

It was the state's most expensive gubernatorial race ever, with Richardson spending $6.7 million, and Sanchez $2.6 million.

Richardson's running mate, Albuquerque businesswoman Diane Denish, becomes the first woman to serve as lieutenant governor in state history.

The Associated Press contributed to this report.