U.S. Sen. Tom Udall of New Mexico is among a group of Democratic senators proposing a constitutional amendment that would give Congress and the states the right to limit campaign contributions and regulate political spending by groups unaffiliated with campaigns.

"Campaigns should be about the best ideas, not the biggest checkbooks," Udall said Tuesday during a Capitol news conference in Washington, D.C. "It's time to put elections back in the hands of American voters, not corporations and special interests."

Udall said the U.S. Supreme Court's "Citizens United" ruling last year, which says the government can't restrict political spending by corporations and unions in candidate elections, is "a threat to our democracy."

But Udall acknowledges amending the U.S. Constitution is an extremely difficult process. And considering that Republicans, who tend to support Citizens United, control the U.S. House of Representatives, getting the measure through the current Congress will be even harder.

Others taking part in Tuesday's announcement were Sens. Chuck Schumer of New York, Dick Durbin of Illinois, Jeff Merkley of Oregon and Sheldon Whitehouse of Rhode Island.

Referring to the Supreme Court's 5-4 decision, New Mexico's junior senator said, "The latest reinterpretation of the Constitution has left our political system vulnerable like never before."

The lawsuit that led to the decision was filed by a conservative nonprofit group that was prohibited in 2008 from buying television time for a documentary attacking Democratic presidential contender Hillary Clinton.

That ruling struck down parts of the McCain-Feingold campaign reform act, which banned "electioneering communications" on television paid for by corporations or labor unions from their general funds in the 30 days before a presidential primary and in the 60 days before the general elections.

Udall said the effects of the decision were apparent in last year's election campaigns. "In 2010 the American people saw a new breed of attack ads from out-of-state super [political action committees]. ... These new organizations raised and spent unlimited funds for the first time since before there was television. And in 2012, there will be even more."

The ads, Udall said, were "overwhelmingly nasty, negative and mean-spirited."

Udall said the proposed amendment would authorize Congress to regulate the raising and spending of money for federal political campaigns, including "independent expenditures" by groups not formally connected to campaigns or political parties. The amendment would allow states to regulate such spending at their level.

He said the amendment wouldn't impose any specific policies or regulations, but instead would allow Congress to pass campaign finance reform legislation that withstands constitutional challenges.

A spokeswoman for Udall said Tuesday that the amendment has nine co-sponsors.

Historically, the method to amend the Constitution has been for both chambers of Congress to pass the amendment with a two-thirds majority. Then, three-fourths of the 50 state legislatures must ratify the amendment. Only 33 amendments have made it through both houses of Congress. Of those, only 27 have been ratified by the states.

There also is a constitutional provision that allows two-thirds of state legislatures to call for a constitutional convention. But that method never has been used.

"Enacting a constitutional amendment is [a] monumental challenge, but doing so is the only way to get to the root of the issue and achieve real campaign finance reform," Udall spokeswoman Marissa Padilla said.

If it does pass Congress, would New Mexico's Legislature ratify such an amendment?

"It probably would stand a better chance after [the 2012] election cycle," said state House Republican Leader Tom Taylor of Farmington on Friday.

That's because, Taylor predicted, new campaign contribution limits in New Mexico are going to drive big contributors "underground" to unaffiliated advocacy groups instead of to individual candidates and political parties.

Taylor said efforts to limit the power of special interests sometimes backfire.

The state campaign contribution limits, which went into effect after the 2010 elections, "neutered the New Mexico Republican and Democratic parties," Taylor said.

And, like Udall, Taylor believes the ads will be even nastier next year.

Taylor said he'd have to see the language of the proposed amendment before deciding whether he'd support or oppose it.

Contact Steve Terrell at 986-3037 or sterrell@sfnewmexican.com. Read his political blog at roundhouseroundup.com.