Princeton, N.J. ? New Jersey’s governors work nearby in Trenton, but the governor’s mansion, Drumthwacket, is here. Tom Kean Jr. was 13 when his father was elected governor in 1981 for the first of two terms. Today the son is 37 and might be crucial to Republicans’ hopes for retaining control of the U.S. Senate.

To capture the Senate, Democrats must gain six seats. So, even if they defeat the five Republicans considered most vulnerable – Montana’s Conrad Burns, Missouri’s Jim Talent, Ohio’s Mike DeWine, Pennsylvania’s Rick Santorum and Rhode Island’s Lincoln Chafee – they will need one more. Perhaps Democratic Rep. Harold Ford, seeking the seat being vacated by Bill Frist’s retirement, will become Tennessee’s first black senator. That would give Democrats the Senate – if they hold all their own seats.

But Republicans might take the one currently held by Maria Cantwell in Washington, or the one from which Minnesota’s Mark Dayton is retiring. Or New Jersey’s seat held by Robert Menendez, 52, who was in his seventh term as a congressman when he was appointed by Gov. Jon Corzine to fill the vacancy created when Corzine resigned to serve as governor.

One of the four reasons Republicans think Kean can win is that appointed senators often are unimpressive candidates for election. Of the 54 other appointed senators in the last 50 years, 15 did not seek election, and 21 of the 39 who did were defeated.

A second reason is New Jersey’s fragrant political culture. Menendez is the first Cuban-American Democrat to serve in Congress, where he was in the House Democratic leadership. He is the third Latino in the Senate (with Florida’s freshman Republican Mel Martinez and Colorado’s freshman Democrat Ken Salazar). But Menendez also is a product of New Jersey’s very American Hudson County, where Boss Frank (“I am the law”) Hague ruled from 1917 to 1949 and gave New Jersey a political template.

On Oct. 15, 1982, a front-page headline in The Jersey Journal, the county’s main newspaper, read: “No Hudson Officials Indicted Yesterday.” Kean laughingly says that when he recently spoke outdoors in Hudson County, he was drowned out by convicts operating lawn mowers – even though the grass had been cut two days before.

Sen. Bob Torricelli dropped out of the 2002 Senate race under a cloud of scandal. Corzine became governor after Gov. Jim McGreevey resigned following after a tangled sexual relationship with a man. Corzine, while a senator, forgave a $470,000 “loan” to a former mistress who was head of a New Jersey public employees union. And there has been much criticism of assistance Menendez gave to a young former staffer: The New York Times reported that he “steered more than $200,000 worth of political consulting and fundraising contracts her way.”

New Jersey voters may just shrug, so inured are they to politics that have produced more than 75 corruption indictments in the last five years. But what is called Menendez’s “baggage” muddies the message as Democrats run against Washington’s supposed “culture of corruption.”

There is a third reason New Jersey Republicans think Kean can win, even though they have not won a U.S. Senate race since 1972, have averaged just 40.7 percent of the votes in the last four presidential elections and trail Democrats in voter registration by 30 percent. The reason is the Kean brand, which is redolent of noblesse oblige, a nice contrast with the state’s more Tony Soprano-style political traditions. Tom Jr., Republican whip in the state Senate, is the grandson of a U.S. congressman, the great-grandson of a U.S. senator and is descended from William Livingston, New Jersey’s first governor.

The fourth reason is that Corzine’s honeymoon as governor lasted but a blink: He has been in office just five months but his sagging approval rating – 39 percent – reflects exasperation with his failure to deliver on his promise of tax relief. Kean suits the state’s social liberalism by being pro-choice and pro-stem cell research, but he favors making the Bush tax cuts permanent, a message that may resonate among heavily taxed voters.

Much may ride on that resonance. A Democratic House would be a nuisance to the president. A Democratic Senate would constrict his remaining sphere for significant domestic accomplishment: With the Judiciary Committee gavel in Sen. Patrick Leahy’s grasp, Democrats could block all judicial nominations from coming to a Senate vote.

In dynastic politics next door, in Pennsylvania, another former governor’s son, Bob Casey, is trying to unseat Santorum. In New Jersey, Republicans fervently hope, the son will rise.