WASHINGTON - Sen. Rob Portman has reached only the halfway mark of his first term as U.S. senator from Ohio, but by the looks of his campaign fundraising, he is taking no chances on his second term. Portman, a Republican, already has amassed a $4.4 million war chest, raising $1.3 million during the last quarter of 2013. He was sworn into office in 2011.

WASHINGTON — Sen. Rob Portman has reached only the halfway mark of his first term as U.S. senator from Ohio, but by the looks of his campaign fundraising, he is taking no chances on his second term.

Portman, a Republican, already has amassed a $4.4 million war chest, raising $1.3 million during the last quarter of 2013. He was sworn into office in 2011.

By comparison, Sen. Sherrod Brown had $1.2 million in his campaign coffers at this point in his term back in 2009. Sen. George Voinovich had $2.1 million in 2007 and Sen. Mike DeWine had $1.6 million at this point in 2003.

Brown, D-Ohio, who won re-election last year after a costly race against Ohio Treasurer Josh Mandel, had $738,446 in the bank as of Dec. 31, according to his campaign-finance report.

Portman’s large total provokes two theories: He’s either trying to safeguard his re-election in an era when outside groups are pouring millions into campaigns, or he’s proving to the GOP presidential field that he can bring home serious cash in the run-up to the 2016 presidential election.

Larry Sabato, a political-science professor at the University of Virginia, thinks Portman is protecting his Senate seat.

“Ohio’s expensive,” he said “and I think he is concerned about a serious primary challenge as well as a tough general election.”

Portman has at least one declared opponent, state Rep. Robert F. Hagan, D-Youngstown, who has raised $5,000 so far in his campaign. Sabato said Portman’s decision to raise scads of money early “ makes perfect sense.”

“The best way to ward off serious opposition is to raise tons of money early,” he said.

But if Portman wants to prove he can bring home cash, he always can point to his position as the National Republican Senatorial Committee’s vice chairman for finance. His job in that role is to raise money for other Republican Senate candidates. He raised $7 million in 2013 in that role. Portman’s leadership political-action committee, the Promoting Our Republican Team PAC, gave nearly $200,000 to state and federal candidates in 2013.

Nathan Gonzales of the Rothenberg Political Report said Portman’s total could be used for any number of things: He could use it for his re-election campaign, use it for a presidential run, or use it to help some of his endangered Republican colleagues.

“It’s always better to have the money and have the option to decide what to do with it, rather than not have it at all,” he said.

jwehrman@dispatch.com