Jim DeMint vividly recalls his first meeting with Marco Rubio two years ago when the youthful speaker of the Florida House came seeking his support for the U.S. Senate. Rubio told how his Cuban refugee parents had worked hotel service jobs all their lives so he and his siblings could have a better life. He spoke of his accomplishments in the Florida legislature (Americans for Tax Reform calls him “the most pro-taxpayer legislative leader in the country”), and unashamedly he explained the guiding force in his life was a commitment to freedom.

Rubio was asking for help from South Carolina’s junior senator because NRSC chairman John Cornyn of Texas had marshaled the backing of the GOP leadership behind Florida governor Charlie Crist—the career politician who just months before had hugged President Obama and embraced his massive stimulus bill. In the days ahead, when DeMint began actively working on Rubio’s behalf, he was 30 points behind in the polls.

Earlier this year Rubio stood before thousands of cheering conservatives as the keynote speaker of the CPAC conference in Washington. Now it was the young Cuban American who held a 30-point lead in the Republican primary polls as Crist prepared to abandon the GOP to run as an independent.

Turning to DeMint on the CPAC stage, Rubio said he would not be there without the help of the South Carolina senator. “He believed in me when .  .  . most of the people who believed in me lived in my house,” Rubio declared.

Rubio is not alone among Republican Senate candidates who owe gratitude to DeMint for helping them oust GOP establishment-backed politicians. In Pennsylvania, there is Pat Toomey, who effectively ended the career of liberal senator Arlen Specter. In Utah it is conservative Mike Lee, who knocked off veteran senator Robert Bennett. In Colorado, Ken Buck; in Kentucky, Rand Paul. Depending on the strength of what appears to be the impending GOP sweep, DeMint may play an important role in the election of eight new Republican senators this fall.

DeMint is a modest man, and he always makes clear that he is by no means the only force behind the seismic shift of power in the Republican party this year. But the story of DeMint’s battle against congressional earmarks, and then against his party’s leadership, has emerged as an important factor in the rise of GOP outsiders in this year’s Senate races. It could be a harbinger of a historic shift in American politics in the years ahead.

DeMint is a most unlikely political crusader. For the vast majority of his life, he had little interest in politics. “I’m a normal guy,” he says with the grin that often crosses his face. He was a family man—a husband and father of four children. He owned a business in his native Greenville, S.C. He was a leader in his church. At various points he served on something like a dozen community boards because to him volunteerism was a way of life.

His profession was marketing, which led him to a career as a consultant. His clients included regional businesses, schools, and hospitals. In his work, he came to see top-down bureaucracy as the enemy of organizational success. And what worked? Empowering front-line employees.

But time would prompt him to see Washington in the same way, as an increasingly bossy and centralized bureaucracy. Complex federal regulations and taxation and expanding government programs were changing America—creating a society of dependents. When DeMint speaks, you hear echoes of the long-ago anti-big government commentaries of Ronald Reagan.

In 1998, at age 46, he decided to run for Congress. He had never run for public office. In a large field of veteran political candidates, he was given little chance of winning. For one thing, DeMint was a passionate free trader in a state whose industrial base had been devastated by the effects of foreign competition. Indeed, DeMint’s support for trade earned him spirited opposition from textile titan Roger Milliken, a powerful funder of conservative causes. (Today, they are friends, and Milliken is a strong supporter of DeMint’s work.)

But when he arrived in Washington to assume his House seat, no one would have pegged him as a troublemaker. He was elected president of his House class and regularly attended seminars given by the House GOP leadership.

But something happened to DeMint in these leadership seminars that would change the course of his life. The gatherings were entirely focused on the means for concentrating and preserving political power: How to milk K Street lobbyists for political contributions; how to place earmarks into appropriations bills so they would be deemed essential to the folks back home.

One day, DeMint had had enough. He rose up in a seminar to question why representatives of the party of smaller government were so focused on earmarks and political fundraising. Why aren’t we talking about reforming the federal tax code or addressing the health care mess?

Midst laughter, someone shouted, “You’ll catch on to the system, DeMint.” But DeMint never did.

In the House, DeMint worked with a handful of serious reformers like Wisconsin’s Paul Ryan, but their bills went nowhere. And when elected to the Senate in 2004, his early work with Tom Coburn for earmark reform appeared an exercise in quixotic futility.

Many of DeMint’s colleagues dismissed his concern over earmarks, arguing they were nickel-and-dime manifestations of traditional politics. But taking a page from the late Robert Novak, DeMint believed that the appropriations system, and the power of appropriators, was the key to runaway spending and taxation and regulation in this country. (Novak likened appropriators to the Vatican’s College of Cardinals.) Without serious appropriations reform, i.e., term limits for appropriators and full transparency for earmarks, there would be no serious tax and spending reform.

To the powerbrokers of Washington, this is political heresy—and makes DeMint a menace. This is why DeMint gives so much credit to Sarah Palin for challenging the machine of the late senator Ted Stevens, because his earmarks​—most notoriously the $400 million bridge-to-nowhere​—symbolized a political system rotten to the core.

In 2006 DeMint assumed the chairmanship of the Senate Steering Committee, a band of conservatives who are an irritant to establishment leaders of both parties in the Senate. He had some good moments. He played a vital behind-the-scenes role in derailing Bush-McCain-Kennedy amnesty for illegal immigrants.

In reality, though, his accomplishments were few. The elections of 2006 and 2008 were disastrous for congressional Republicans. In long talks with his wife Debbie, he contemplated packing it in rather than running for reelection in 2010. He was convinced that nothing was going to change in Congress unless the very nature of go-along-to-get-along Republicans changed.

It was these conversations that led DeMint to one of the most radical departures from decorum in the history of the Senate. DeMint decided to create a new campaign and serious funding mechanism (the Senate Conservatives Fund) to support reform candidates for the Senate—even if that meant ousting prominent members of the hallowed Senate club.

That is how Marco Rubio came to the office of South Carolina’s junior senator.

Will newly gained political power lead DeMint to seek an overthrow of Mitch McConnell or John Cornyn and the Senate Republican leadership? Those close to DeMint say his efforts are not motivated by a desire for a spot in the leadership office.

But a sense of determination comes over this modest, small town Southerner as he reflects on Republicans in the Senate. “Members must know that if they oppose changing the grip appropriators hold over the process, they will face grassroots opposition that may cost them their seats,” he says. “We don’t need to reform earmarks, we need to eliminate them.”

The seemingly all-powerful Washington political class is taking DeMint a lot more seriously these days.

Kenneth Y. Tomlinson is a former editor in chief of Reader’s Digest.