Sen. Bob Casey has more at stake this year than his own re-election.

As the reticent leader of Pennsylvania Democrats, the first-term Senator also serves as President Barack Obama’s top lieutenant in the vital Keystone State.

“I think the responsibility or the effort is heightened when it’s a presidential year,” Casey said in an interview last week. “It’s a little bit difficult when you’re also running. So that’s a challenge.”

Observers say that Casey, the son of a popular former governor who took over as the state’s highest-ranking Democrat after former Gov. Ed Rendell left office earlier this year, is up to the task. In the early ’90s, Casey’s namesake ruled Harrisburg with red-faced tenacity — the opposite of Casey’s low-key, monotone style. The late governor didn’t often get his hands dirty in state party politics, instead focusing on his opposition to abortion rights as his singular issue.

Casey doesn’t have that luxury — at least not this cycle. Although he is the heavy favorite to win re-election, he’s running against a Republican with significant financial resources while also balancing the demands of helping to ensure Democrats deliver the state for Obama.

“He’s the most senior Democratic official, and he’s taking it seriously,” Rep. Allyson Schwartz (D-Pa.) said in a June 1 interview. “These are not mutually exclusive — in fact, quite the opposite. They are very compatible — to make sure there is good state turnout, and that there is turnout for the president and for him, up and down the ticket.”

In the past two years, the Pennsylvania Democratic Party’s staff has quadrupled. To attract top political talent, party officials moved the bulk of the staff to Philadelphia, a much more desirable city for top operatives than its former base in the capital of Harrisburg.

Casey has played a role in all of this and personally helped to recruit the party’s challengers in the 8th and 18th districts, two targets for national Democrats this fall. He’s picked sides in primaries occasionally, such as backing Obama in 2008 and endorsing Rep. Tim Holden’s failed Democratic primary bid earlier this year.

But the soft-spoken Casey is hesitant to discuss his partisan activities in any detail. He only acknowledges the challenge of running a state party in transition all the way from Washington, D.C. — something his father never had to do.

“When you have a governor of your party, that governor has the capacity to be able to build a party, lead a party, more so than any Senator or anyone in the Congressional delegation,” Casey said. “When you have a transition to the governor of the other party, that creates certain challenges.”

Casey has other things to worry about.

In 2006, he defeated former Sen. Rick Santorum (R) by a whopping double-digit margin. Current polls show Casey with a similar lead, but local operatives don’t expect him to win by such a hefty number in November.

In his Russell building office, Sen. Ron Johnson’s doorway is just steps from Casey’s. The proximity serves as Casey’s constant reminder of just how quickly a campaign can go downhill against a deep-pocketed opponent.

Within a matter of six months in 2010, then-Sen. Russ Feingold (D-Wis.) watched his re-election prospects slip away as the result of Johnson’s ability to capitalize on voter angst and dissatisfaction with Congress. The Wisconsin Republican spent $8.9 million of his own money on the race and defeated Feingold by 5 points.

In November, Casey faces Tom Smith, a former coal company executive who spent $5 million on the GOP primary. And there’s more where that came from.

In a Wednesday interview, Smith estimated his race will cost $20 million but declined to say how much of that he will self-fund.

“In the very slight case that we can’t raise sufficient [funds], I will say this: That well of money is not near dry yet.”

Smith has met with Johnson, as well as freshman Rep. Mike Kelly (R-Pa.), a first-time candidate and successful businessman who won an Erie-based seat last cycle.

“Sen. Bob Casey has a famous name, political name in Pennsylvania. I concede that point,” Smith said. “But he is not his father, and he now has a voting record that he will need to defend.”

Compared with his father, Casey is much more of a team player in Democratic Party politics — a liability that might come back to haunt him if the president’s poll numbers don’t hold up in Pennsylvania.

His father never played the local or national political party game. In fact, Casey’s congenial leadership style couldn’t be more different from his forceful and hot-headed father.

The Senator’s older sister famously told the Philadelphia Inquirer in 2002 that her brother bought a mood ring in the 1970s and it “never changed color.” Former Lt. Gov. Mark Singel, who served under the elder Casey from 1987 to 1995, described a boss who was “able to disintegrate you with an icy stare-down if he had to.”

And unlike his son, the former governor made his opinions known even among his closest allies. During the health care debate of the early 1990s, Gov. Casey trekked to Washington, D.C., to persuade newly appointed Sen. Harris Wofford
(D-Pa.), to vote for an anti-abortion-rights amendment. After a heated argument lasting more than an hour, the governor stated he could not support Wofford’s re-election bid against Santorum, who went on to win.

“I think Bob Casey the Senator is much more engaged with state party politics,” Singel said. “Bob Casey Jr. has the same capabilities and knowledge but has matured in his political persona so that he doesn’t have that kind of cold streak in him. He either doesn’t have it or has hidden it well.”