BIG SKY, Mont. (AP) — Stark disagreement over the Citizens United campaign finance ruling highlighted Montana’s first U.S. Senate debate on Saturday, as Republican challenger Denny Rehberg defended the Supreme Court decision as vital to free speech.

Incumbent Democrat Jon Tester responded that the widely criticized ruling puts democracy at risk by giving corporations more power than people.

The Montana Newspaper Association debate marked the first time the two candidates have faced off in person after more than a year of campaigning. Control of the Senate is potentially at stake in one of the nation’s most-watched races.

The two candidates offered starkly divergent views on issues ranging from health care to student loans to regulation of the financial industry.

Rehberg persistently hammered his opponent as a front-man for the Obama administration. Tester touted legislation he sponsored or supported to help seniors, veterans and the uninsured.

But the divide over Citizens United stood out. The Supreme Court ruling undid past restrictions on political spending by corporations and special interest groups. It’s been derided by many Montana politicians.

Rehberg said he supported the ruling, although he added that there should be full transparency on where campaign money is coming from.

“There should be nothing more free than political free speech,” he said.

Tester responded that “corporations are not people.”

“Because of Citizens United, corporations have more rights when it comes to donations than people do,” he said.

First-term incumbent Tester, a 55-year-old self-described “dirt farmer” from Big Sandy, narrowly won six years ago. He’s since tried to solidify support by appealing to a broad range of voters including veterans, seniors and women.

But Rehberg, 56, is a formidable opponent who already enjoys statewide name recognition after six terms as Montana’s sole member of the House.

The campaign is destined to become the most expensive in Montana history.

On top of special interest money pouring in, the two candidates combined have raised almost $12 million and spent more than $5.6 million, according to the latest finance reports from their campaigns. Analysts say total spending could easily top $20 million.

The issues at play so far in the race — including the deficit, tax policy, jobs and natural resource development — offer a microcosm of the national political divisions among Republicans and Democrats.

There are more than four months to go before the election, and many voters remain tuned out, said Montana State University political scientist David Parker. But for the campaigns and the reporters covering the race, Parker said the debate could set the tempo for coming months.

“Both of them stuck to their messages,” he said. “They differ obviously, but the state of Montana has two really solid candidates.”

Also participating in Saturday’s debate was Libertarian candidate Dan Cox of Hamilton.

Calling his opponents “two sides of the same coin,” Cox said Democrats and Republicans bear equal responsibility for the nation’s economic ills. If elected, he pledged to “cut cut cut” to rein in spending.

“If we don’t get our deficit under control, if we don’t stop printing money, we’re going to go bankrupt,” Cox said.

Cognizant of public distrust of Congress, Cox’s opponents stressed their willingness to break ranks with the party line when it’s in Montana’s best interest.

Tester dismissed claims that he’s sided with Obama and the Democrats on the vast majority of issues. He cited the auto industry bailout, proposals to regulate farm dust and youth labor and the removal of wolves from the endangered list as instances when he’s gone against members of his party.

Rehberg spoke of the need for “Montana solutions” and declared his support for government assistance to ensure rural areas of the state are provided adequate highways and air and train service.

The otherwise civil debate took a personal turn in the closing minutes as Tester questioned Rehberg’s credentials as a rancher. Rehberg and his wife family have made tens of millions of dollars subdividing and selling pieces of their Billings ranch for housing developments.

“Farming and agriculture is part of my blood,” said Tester. “Building houses is not ranching.”

Rehberg said after the debate that he was leasing his ranch but still plays a role in the operation. He added that his wife, Jan, owns the family real estate business and said Tester “just attacked all women who run their own businesses.”