WASHINGTON -- A long-shot lawsuit challenging the Senate filibuster rules, in part over a contentious immigration issue, was tossed out Friday by a federal judge.

In a 47-page ruling, U.S. District Judge Emmet G. Sullivan acknowledged that the "filibuster rule is an important and controversial issue . . . as in recent years, even the mere threat of a filibuster is powerful enough to completely forestall legislative action."

Nonetheless, Sullivan added that he was “powerless to address this issue” for several reasons.

"Reaching the merits of this case would require an invasion into internal Senate processes at the heart of the Senate’s constitutional prerogatives as a House of Congress, and would thus express a lack of respect for the Senate as a coordinate branch of government,” Sullivan wrote.

The government watchdog group Common Cause filed the lawsuit on behalf of itself and several members of the House of Representatives, who contended Senate Republicans had used the filibuster to block campaign finance reform legislation. Joining the suit were three individuals who said they would have benefited from the so-called DREAM Act had it not been blocked by a filibuster.

Erika Andiola, Celso Mireles and Caesar Vargas, who were born in Mexico and now live in the United States, said the stalled immigration legislation could have helped them attain legal U.S. status had the bill not been blocked.

Sullivan, though, found they lacked the legal standing to sue and said they "failed to demonstrate" that the immigration bill or campaign finance reform bill would have passed if it weren’t for the filibuster.

Among other things, the filibuster requires a vote of 60 senators before the Senate can proceed with or end debate on bills. The lawsuit argued it is unconstitutional because it is “inconsistent with the principle of majority rule.”

Undeniably, the filibuster has become an obstructive tool commonly deployed by members of the minority party.

“The number of actual or threatened filibusters has increased dramatically since 1970, and now dominates the business of the Senate,” Sullivan acknowledged.

In 2009, the Senate counted a record 67 filibusters, which was double the number of filibusters that occurred in the entire period between 1950 and 1969. For the whole 111th Congress, which spanned 2009 and 2010, the number of filibusters had increased to 137.

As a result, Sullivan said, “many (bills) with broad bipartisan support died in the Senate without ever having been debated or voted on because of the inability to obtain the 60 votes.”

Nonetheless, Sullivan noted that he was “not in a position . . . to determine or predict what action the Senate might take in a final vote” on either the campaign finance or immigration bills.

Sullivan’s ruling followed oral arguments Dec. 10. It is not, however, the end of discussion about revising the filibuster. Separately, Senate Majority Leader Harry Reid of Nevada has spoken publicly about potential filibuster reforms that might be tried at the start of the 113th Congress next month.