(Fixes typo in Barack in first paragraph) *Democrats have potential to clear Republican hurdles *Obama still faces challenges in passing major measures By Thomas Ferraro WASHINGTON, July 7 (Reuters) - Democrats achieved their biggest majority in the U.S. Senate in decades on Tuesday as Al Franken of Minnesota finally took his seat -- but President Barack Obama will still have to fight hard to muster the votes to pass healthcare reform and other major initiatives. Franken, who won the seat after a 239-day recount and legal battle following last November's election, became the 60th member of the Senate Democratic Caucus. That gives them the potential to clear Republican procedural hurdles, confirm presidential nominees and pass legislation without a single Republican vote if they stick together. Yet regional and philosophical differences among Obama's fellow Democrats mean the president must continue to work hard to unite his own party behind him. The biggest challenges remain healthcare reform and climate change legislation, both seen by conservatives as huge new burdens for a government already stretched by record deficits. "I am under no illusions that suddenly I'm going to have a rubber-stamp Senate," Obama said earlier this year in anticipation of Franken winning the seat. Franken took the oath in the Senate after dozens of Democrats and a few Republicans shook his hand and then joined in an ovation. He was assigned to a handful of Senate panels, including the Judiciary Committee that will begin confirmation hearings next week on Supreme Court nominee Sonia Sotomayor. The comic-turned-politician was sworn in a week after the Minnesota Supreme Court upheld his razor-close win over Republican Norm Coleman. COMPLICATED CALCULATIONS With 58 Democratic seats and two independent allies in the Senate caucus, Democrats are as strong as they've been since 1981. They should be able override Republican stalling tactics known as filibusters -- but only if they stick together. The calculation is further complicated by the failing health of two senior Democratic lawmakers, Edward Kennedy and Robert Byrd, whose frequent absences will force Democrats to continue seeking Republican votes. Moderate Republican Senators Olympia Snowe and Susan Collins, both of Maine, have crossed party lines before and Obama hopes they occasionally do so again. Ethan Siegal of The Washington Exchange, a private firm that tracks Congress for institutional investors, said there are about 20 Senate Democratic "centrists" who could present problems on various matters for the president. "They don't move as a herd," Siegal said. Still, Stephen Hess, a congressional scholar at the Brookings Institution, says the 60-seat threshold could provide Obama a lift by "creating the impression that the president is in the catbird seat." But Hess said senators, by nature, see themselves as representing a co-equal branch of government and don't like to be considered in the pocket of any president. Democrat Ben Nelson, a prominent moderate, said he did not know if the "supermajority" will impact any legislation. "Things will be decided issue by issue by issue," Nelson said. "There are a lot of us who have strong feelings about various programs, whether it's health care, energy or climate change." Senator Joseph Lieberman, a former Democrat turned independent, said, "There will still be a struggle most every time (on major issues) to get 60 votes to break a filibuster."It's the nature of the Senate." (Editing by Alan Elsner)
