WASHINGTON – Congress returns for its midsummer session Monday with a Senate supermajority not super enough for President Obama’s top priorities to pass without Republican support.

The seating of Minnesota Sen. Al Franken will give Democrats the filibuster-proof 60-40 majority in the Senate, but only on paper.

Absences by two ailing senators mean the party can count only 58 votes, and then only if Majority Leader Harry Reid can herd two independents and the independent streaks of 55 others behind Obama’s biggest initiatives: expanded health care coverage and cleaner but more expensive energy.

Republicans are well aware that the closer the Democrats get to 60, the more leverage GOP senators have as Congress struggles with those problems that have eluded solutions for decades.

“With their supermajority, the era of excuses and finger-pointing is now over,” said GOP Sen. John Cornyn of Texas, who heads the National Senatorial Republican Committee.

It’s a fragile supermajority because Sens. Robert Byrd of West Virginia and Edward Kennedy of Massachusetts are ill and have not voted in weeks. Byrd, 91, returned home last week from a six-week hospital stay after a series of infections. Kennedy, 77, is battling brain cancer.

Ill senators have voted by gurney and wheelchair in the past. But Democrats and Republicans said they don’t foresee any votes this week that would be close enough to warrant a trip to the Senate by either Byrd or Kennedy.

It’s a truism that it’s often easier to get 80 votes and more than it is to get 60. Overwhelming support for legislation can become a persuasive force of its own. But senators have various reasons for trying to stop or slow a bill – typically regional matters, ideology and plain self-interest – that might overrule party loyalty.

Thus, Obama, Reid and Co. have much legislative horse-trading ahead of them on an assortment of items poised for consideration before Congress’ monthlong August break.

Slowing it all down will be Senate hearings and debate on appeals court judge Sonia Sotomayor’s fitness for the Supreme Court. Senate Judiciary Committee hearings are set to begin July 13, followed by what’s expected to be a robust two weeks of committee and floor debate.

Democrats want her confirmed before Congress leaves for its summer vacation. Republicans have complained that her nomination is moving too fast.

On policy, Democrats in the House and Senate are pushing to begin votes by month’s end on health care. Obama has urged Congress to finish work by the end of the year on the bills designed to control health costs and make coverage available to about 47 million people who lack it.

Senate committees are set to tackle an energy bill that aims to reduce greenhouse gases blamed for global warming. Here, regional divisions among Democrats undermine leaders’ prospects of nailing down 60 votes in favor of it.

Sen. Barbara Boxer, D-Calif., has the Senate Environment and Public Works Committee writing a global warming bill. It’s using the House plan, which calls for a 17 percent reduction in greenhouse gases by 2020 and an 83 percent reduction by 2050, as a starting point.

Also on the July agenda are more House and Senate votes on the 12 annual spending bills for the budget year that begins Oct 1. The House has passed four of the 12; the Senate is scheduled to vote Monday on its first, covering what Congress spends on its own operations.

House leaders promise to try to pass all 12 bills by the end of July. Action in the Senate promises to be slower.