By John Simons

(FORTUNE Magazine) – WHEN JON CORZINE WAS FORCED OUT as co-CEO of Goldman Sachs in 1999 and breezed into his New Jersey Senate seat in 2000, most politicos saw the tall, bearded, former Illinois farmboy as a political dilettante, albeit one worth $400 million. Four years later, however, Corzine has proved to be no dabbler. The 57-year-old Senator has eased his way into the Democratic Party's inner sanctum, in part by bringing Democratic fundraising on par with Republican efforts for the first time in three decades. As a result Corzine has become one of the party's most sought-after sages on economic policy, and his name is even being floated as a possible Treasury Secretary in a Kerry administration. Expect to see more of Corzine this fall, as the Kerry campaign plans to use him to go after Bush.

For the past year Corzine has been an important liaison between the party and wealthy Democratic backers on Wall Street, while at the same time serving as a backroom economic advisor and spokesperson for the Kerry-Edwards campaign. Democrats in New Jersey had hoped Corzine would enter the November gubernatorial election to serve the remaining 14 months of outgoing governor Jim McGreevey's term. Corzine held off, insisting he'd prefer to wait until the scheduled 2005 race. That decision conveniently buys him some time and, in the event of a Kerry victory, gives him a possible shot at that Treasury job. Gene Sperling, senior economic advisor to the Kerry-Edwards campaign, calls Corzine a policy innovator and says he's come into his own as a "thinker," especially on the issues of fiscal discipline and Social Security. Corzine takes part in frequent conference calls with Kerry and his advisors and has also helped Kerry fashion a proposed policy that would eliminate tax incentives for corporations that send jobs overseas. (For another take on the candidates' economic policies, see Geoffrey Colvin's column in this issue.)

Corzine is mildly flattered by all the attention, though he is well aware that there are other equally qualified candidates to head a Kerry Treasury. Roger Altman and Gene Sperling, for instance, are the Kerry campaign's official economic gurus. Both are being mentioned for the Treasury job, along with Robert Rubin (who is more likely to be Kerry's pick to helm the Federal Reserve should Alan Greenspan retire).

Corzine's newfound power mostly has to do with his fundraising prowess. In 2002, Democrats put him in charge of aiding their efforts to regain a majority in the Senate. He quickly moved to overhaul the Democratic Senatorial Campaign Committee's (DSCC) fundraising arm in order to take advantage of the new campaign-finance laws. He hired a market research firm and a data-modeling company to help the party locate new small donors, and he personally traveled the country soliciting individual donations from CEOs and other business leaders. The DSCC's haul in the current election cycle ($51.3 million) is comparable to Republican efforts ($54.9 million).

As a Treasury Secretary, Corzine would be a fiscal conservative. In the Senate he's been a vocal critic of Bush's Medicare overhaul and of White House efforts to privatize Social Security. He helped draft Sarbanes-Oxley and also fashioned his own bill to crack down on mutual fund abuses. Corzine is particularly vocal about the mounting national debt. "We clearly have to deal with our deficit and the structure of our fiscal policy. Are we going to reduce the role of government or entitlements?" He adds that with the next President facing such tough financial choices, "We need a little bit of Ross Perot-type frankness here." Could Corzine be the person to deliver that dose of reality? "Anybody who's spent a lifetime in finance would seriously consider the Treasury. It would be quite an honor," he says. For now, Corzine must focus on a different set of figures: Kerry's poll numbers. -- John Simons