Washington (CNN) -- Sen. Arlen Specter's decision to leave the Republican Party in April handed President Obama a key vote in the Senate, and Specter was rewarded by quickly being endorsed by the president and Democratic leaders in his bid for re-election next year.
But not every Democrat got in line behind Obama.
In Kentucky, GOP leaders spent the first half of the year hoping that Sen. Jim Bunning would retire, thereby allowing a more popular Republican to run and giving the GOP a better chance to hold onto the seat.
For months, Bunning refused to say he was retiring, but by midsummer the Hall of Fame baseball pitcher relented and provided Republican leaders an opening to rally around the candidacy of Kentucky Secretary of State Trey Grayson.
But not every Republican got in line behind the GOP establishment.
Primaries are complicating matters for Democratic and Republican Senate leaders, who would prefer to focus all of their attention on the 2010 general election, not internal battles for party nominations. Republicans have more primaries to sort out than Democrats next year, but Democrats have their own set of issues to address in the midterm elections.
A lot is riding on the 2010 Senate contests: Obama's future, the Democratic Party's future, the Republican Party's future, and the political careers of lawmakers who have made the Senate their home and those who want to call the "World's Most Exclusive Club" home.
Heading into 2010, Democrats must defend 19 seats, which includes an opening that occurred when Massachusetts Sen. Edward Kennedy died. A special election for Kennedy's seat will take place in January. Republicans must protect 18 seats. And Democratic and Republican strategists are quick to point out opportunities to pick up seats that the other party now controls.
In the Senate, the magic number is 60. It takes 60 senators to break a filibuster. Thanks to Specter's defection and the fact that two independents align themselves with the Democratic Party, Democrats control 60 votes. In theory, Obama should be able to marshal his legislative agenda through the chamber. But as we are witnessing in the debate over health care reform, 60 is just a theoretical number, and for the president to overcome obstacles in the Senate -- yes, even hurdles erected by members of his own party -- he needs more than 60 votes to win on the more contentious issues.
The task of getting Democrats elected falls to Sen. Robert Menendez, D-New Jersey, who serves as chairman of the Democratic Senatorial Campaign Committee in this two-year election cycle. "We are going to do everything to preserve our present majority and try to build on it," he said in an interview.
While the chairmanship of a political party committee can be a thankless task -- frequent travel and constant fundraising -- it appeared at the beginning of the year that Menendez would have an easy job. Democrats had just picked up at least seven seats, Obama's approval rating was soaring, and in the reliably Republican state of Georgia, Sen. Saxby Chambliss needed a runoff to win re-election.
Conversely, Republicans were down in the dumps. "Despondent is probably a better word," to describe the GOP's mood, said Sen. John Cornyn, R-Texas, chairman of the National Republican Senatorial Committee, Menendez' political counterpart.
"We had just been beaten very badly in a national election that depleted our numbers in the Senate and House and elected Barack Obama to the White House," Cornyn said.
To make matters bleaker for the GOP, Specter switched parties, and the unresolved Senate race in Minnesota was finally called in favor of Democrat Al Franken. Democrats had the 60 votes they had coveted.
But as the summer wore on, the future did not look as dark for Republicans. Obama's soaring favorability rating dropped -- it has now settled back to an earthly 55 percent. The Democratic Party's signature domestic issue, health care reform, was in a critical state, and Republicans finally settled on a message of fiscal responsibility.
Then the GOP got some additional good news, when cracks in the veneers of two Senate veterans were exposed. Early polling showed that Majority Leader Harry Reid, D-Nevada, and Sen. Chris Dodd, D-Connecticut, were in danger of losing re-election battles in 2010. And additional surveys indicated that Republicans had a legitimate chance of picking up the seats once held by Obama and Vice President Joe Biden.
