Updated: Even before their Massachusetts victory this week, Republicans enjoyed a multitude of advantages in this year’s midterm elections. The Supreme Court has most likely just delivered one more: money.

Today’s ruling upends the nation’s campaign finance laws, allowing corporations and labor unions to spend freely on behalf of political candidates. With less than 11 months before the fall elections, the floodgates for political contributions will open wide, adding another element of intrigue to the fight for control of Congress.

At first blush, Republican candidates would seem to benefit from this change in how political campaigns are conducted in America. The political environment – an angry, frustrated electorate seeking change in Washington – was already favoring Republicans. Now corporations, labor unions and a host of other organizations can weigh in like never before.

But the populist showdown that was already brewing – President Obama on Thursday sought to limit the size of the nation’s banks – will surely only intensify by the Supreme Court’s ruling. The development means that both sides will have even louder megaphones to make their voices and viewpoints heard.

Mr. Obama issued a statement – a rare instance of a president immediately weighing in on a ruling from the high court – and said his administration would work with Congressional leaders “to develop a forceful response to this decision.”

“With its ruling today, the Supreme Court has given a green light to a new stampede of special interest money in our politics,” Mr. Obama said. “It is a major victory for big oil, Wall Street banks, health insurance companies and the other powerful interests that marshal their power every day in Washington to drown out the voices of everyday Americans.”

Republicans, of course, hailed the ruling as a victory for the First Amendment.

“I am pleased that the Supreme Court has acted to protect the Constitution’s First Amendment rights of free speech and association,” said Senator John Cornyn of Texas, chairman of the National Republican Senatorial Committee. “These are the bedrock principles that underpin our system of governance and strengthen our democracy.”

Democrats, not surprisingly, said the ruling would be bad for democracy.

“Giving corporate interests an outsized role in our process will only mean citizens get heard less,” said Senator Robert Menendez of New Jersey, chairman of the Democratic Senatorial Campaign Committee. “We must look at legislative ways to make sure the ledger is not tipped so far for corporate interests that citizens voices are drowned out.”

Senator Russ Feingold, one of the architects of the 2002 campaign finance restrictions known as the McCain-Feingold law, issued this reminder that the court’s decision did not completely lift some boundaries for corporate money:

“It is important to note that the decision does not affect McCain-Feingold’s soft money ban, which will continue to prevent corporate contributions to the political parties from corrupting the political process. But this decision was a terrible mistake. Presented with a relatively narrow legal issue, the Supreme Court chose to roll back laws that have limited the role of corporate money in federal elections since Teddy Roosevelt was president. Ignoring important principles of judicial restraint and respect for precedent, the Court has given corporate money a breathtaking new role in federal campaigns. Just six years ago, the Court said that the prohibition on corporations and unions dipping into their treasuries to influence campaigns was ‘firmly embedded in our law.’ Yet this Court has just upended that prohibition, and a century’s worth of campaign finance law designed to stem corruption in government. The American people will pay dearly for this decision when, more than ever, their voices are drowned out by corporate spending in our federal elections. In the coming weeks, I will work with my colleagues to pass legislation restoring as many of the critical restraints on corporate control of our elections as possible.”

No word yet from his partner on these initiatives, Senator John McCain, Republican of Arizona.

As Mr. Feingold’s statement expressed, these early comments are the opening volley in a battle expected to quickly begin on Capitol Hill, as Democrats push for new legislation to put some of the campaign finance restrictions back in place.

In the meantime, citizens, brace yourselves. An even more intense barrage of advertising and advocacy – on television, the Web and beyond – will be at hand in the 2010 midterm elections. Information overload awaits …