Barack Obama’s to-do list is long. But if the Illinois senator wins the presidency in November, he may just confront one of the more painful lessons in US politics: change in Washington often dies when it reaches the Senate. Congress’ upper house is often called the world’s greatest deliberative body – a statement not always meant as a compliment, especially when a new president wants to pass legislation quickly. Obama’s ability to achieve his promised changes will likely hinge on the 100 men and women of the US Senate.

When George Washington and friends designed the US system of government, they intentionally created two distinct legislative bodies. The founders wanted the House of Representatives to reflect the will of the American people. Congressmen face election every two years and, with frequent turnover, the majority rules the institution. Legislation moves quickly through its corridors.

Members of the Senate, by contrast, serve six-year terms, and the Senate was designed to be dramatically different from the House. Upon his return from his diplomatic post in France, Thomas Jefferson asked George Washington why the Constitutional Convention created a Senate. ‘Why did you pour that coffee into your saucer?’ asked Washington. ‘To cool it,’ said Jefferson. ‘Even so,’ responded Washington, ‘we pour legislation into the senatorial saucer to cool it.’

Senators in the minority have a full china cabinet at their disposal to cool the agenda of the ruling party. The most notorious is the filibuster – the tactic of talking a bill to death by prolonging debate indefinitely. In 1957, South Carolina senator Strom Thurmond spoke for over 24 hours in an unsuccessful attempt to kill the Civil Rights Act of 1957. But there are other, less physically demanding, ways to kill a bill. Any senator can indefinitely block legislation from coming to a vote by requesting a ‘hold,’ and it can be demanded for any reason – to negotiate changes, review a bill, or simply to kill it. In the last two years, Republican senator Tom Coburn of Oklahoma has requested more than 80 holds – earning him the nickname ‘Doctor No,’ a title he proudly wears as a member of the minority Republican party. It’s lawmakers like Coburn whom a President Obama will likely have to overcome if he pursues greener environmental laws, stricter trade deals and universal health care.

Or will he? ‘Holds,’ filibuster and the minority can be bypassed if 60 or more senators vote to bring debate on bill to an end. With a slim majority of just 51 senators currently, Democrats have been unable to muster the three-fifths needed to push their legislative agenda. Until just recently, few Democratic strategists realistically expected the 2008 election to deliver a filibuster-proof majority. But shifting political winds in traditionally conservative states and a fresh round of Republican political scandals may prevent a President Obama from ever having to feel the pain of Senate’s tedious pace.

Democrats begin this election cycle in a position of power. Of the 35 seats up for election in 2008, 23 are held by Republicans and 12 by Democrats. Virginia, Colorado, New Mexico and Alaska are all traditionally conservative states, currently with Republican senators, that will almost certainly elect Democrats this fall. The first three are so-called purple states, where a flood of new immigrants and suburbanites have changed state politics and given Democrats an edge in recent years. Alaska, while still thoroughly conservative, has been rocked by the recent indictment of Senator Ted Stevens, the Senate’s longest serving Republican, on federal corruption charges.

But Republican troubles do not end there. New Hampshire, Minnesota, Oregon, Mississippi, Maine and North Carolina are all states also with Republican senators, but polls show the Democratic challengers within striking distance. Those elections are up for grabs. Republicans might expect to hold on to North Carolina and Mississippi, but with large African-American populations, Democrats hope that Obama will generate record turnout among black voters that provide them an edge in November. Most importantly for Democrats, the only Senate seat they currently hold that might give them heartburn this fall is Louisiana. But while Senator Mary Landrieu is in a tight race with her Republican challenger, she has held the seat since 1996 and is reasonably popular.

With John McCain running away from President Bush and the Republican ‘brand’ in general, Democrats on Capitol Hill are more optimistic than ever that they might reach 60 seats and record a massive victory in the Senate. And even if they come up just short, their ability to tempt moderate Republicans to their side on key legislative battles will be greatly improved, and might give Obama the muscle to push through many of his campaign promises.