Sen. Frank Lautenberg (D-N.J.), the oldest member of the Senate, died early Monday of complications from viral pneumonia, his office said. He was 89. Lautenberg had battled stomach cancer and other illnesses in recent years.

Lautenberg's health had been failing for months, and he missed several key votes. But he made a dramatic return to Capitol Hill in April to vote for bills aiming to reduce gun violence, an issue he was passionate about. Lautenberg went to the Senate floor in a wheelchair, and called out "aye" in support of expanded federal background checks for gun buyers. The measure failed, however, as did Lautenberg's amendment seeking to ban high-capacity ammunition clips.

Lautenberg was a World War II veteran and successful businessman first elected in 1982, when he was 58 — an age when "when most people are planning retirement," notes Ed Kilgore at Washington Monthly. He established a consistently liberal record over a long but low-key career in the Senate, writing some of the nation's most sweeping health and safety laws. He retired briefly after three terms, then had a change of heart and jumped back into politics in 2002 after fellow Democrat Robert Torricelli, facing ethics troubles, decided against running for re-election at the last minute.

The late senator's legislative victories began piling up in 1984, when, as a freshman, he pushed through a measure establishing a national drinking age of 21 and threatening to slash highway funds for states that didn't comply. He also led the effort to ban smoking on commercial airline flights, as well as in all federally financed buildings serving children.

Admirers mourned Lautenberg as one of the left's unsung heroes. Sen. Kristen Gillibrand (D-N.Y.) tweeted that Lautenberg was "such a champion on so many issues close to my heart. He will truly be missed." Here's Steve Benen at MSNBC, echoing sentiments expressed by many liberal commentators:

The U.S. Senate lost one of its great progressive champions this morning...

Despite his failing health — Lautenberg's presence in the Senate has been intermittent in recent months — the New Jersey Democrat was nevertheless still active in governing, championing gun reforms earlier in the spring and co-sponsoring a new bill modernizing the Toxic Substances Control Act. [MSNBC]

As his health failed and Newark Mayor Cory Booker revealed that he planned to run for Lautenberg's seat in 2014, Lautenberg announced in February that he wouldn't seek re-election. He had hoped to be able to see through a few final accomplishments in the remainder of his term, however, and managed to forge a bipartisan compromise on one of them last month — a bill overhauling a law regulating chemicals used in household products.

Friends and former colleagues said the Democrats have lost a dedicated advocate for some of the party's central causes. Carter Eskew, who worked for Lautenberg in his first campaign, writes in The Washington Post that Lautenberg's confidence and determination were apparent from the moment he entered politics when, as a political neophyte, he defied the odds and swept aside a political legend, Millicent Fenwick.

No one thought Frank could win, except Frank. He always had a swagger, a chip the size of Newark, before it shrunk, on his shoulder. Frank could get in your face and up in your grill. He was born in the same New Jersey area as Rubin Carter, and like Hurricane, Frank liked to fight. [Washington Post]

Now, New Jersey Gov. Chris Christie, a Republican, will get to appoint someone to fill the seat until a special election is held, probably in November. Then another election will be held in 2014 for the full six-year term. If, as many expect, Christie chooses a Republican, the Democrats' majority in the Senate will narrow, leaving them with just 52 of the 100 seats, plus two independents who tend to caucus with the Dems. Rick Moran at American Thinker notes, however, that the position probably won't be in the GOP's hands for long.

Whoever [Christie] chooses will have a leg up should they choose to run for the GOP Senate nomination.

But as far as the general election, the Republicans will be at a disadvantage. They haven't won a Senate race in New Jersey since 1972. [American Thinker]