With a costly and caustic rescue of Sen. Lincoln Chafee in Tuesday’s primary, the Republican Party kept alive at least the hope it can retain his seat in the November US elections.

In Rhode Island and in 2006, mark that down as an accomplishment for a party struggling to maintain Senate control.

“Our goal has always been to find the common ground for the common good,” said Chafee, whose independence is his political calling card. “Partisan politics must not prevail,” he added.

Fine for him to say. Without partisan politics, the outcome might well have been different, his career over and Democrats celebrating the capture of his seat before the election campaign had fairly begun. Democrats must gain six seats to capture control of the 100-seat Senate. The Republicans dispatched money and manpower to Rhode Island in a political version of good-cop, bad-cop.

The party’s senatorial committee battered Chafee’s conservative primary rival, Stephen Laffey, with television advertising and mail of the type normally unleashed against a Democrat. The Republican National Committee moved in with a get-out-the-vote operation that added thousands of Chafee-inclined moderates to the conservative Republican electorate.

The result was a surge of voting by independent, moderate Rhode Islanders of the type Chafee himself had said was essential to his success. “If it’s low, I’m behind. If it’s medium it’s close. If it’s high, I’m ahead,” he said of voter turnout two weeks before the election.

For all the effort, Chafee’s primary victory merely sends him onto a campaign against Democrat Sheldon Whitehouse, former Rhode Island attorney general. Sen. Chuck Schumer, Democrat, in charge of the Democratic senatorial committee, said the primary portends a tough fight in the November.

“When Lincoln Chafee — an incumbent Republican senator — can barely win his own primary, you know he’ll have trouble in the general election,” he said.

Neither Chafee nor Republicans disputed that. But the alternative was far worse, as the Republicans saw it. Sen. Elizabeth Dole, who heads the Republican senatorial campaign committee, had decided to leave Laffey on his own in the fall had he won the primary, essentially surrendering the seat to the Democrats.

Instead, she issued a statement congratulating Chafee on his victory. His “independent, honest leadership drove a historic turnout and clearly shows he is in a great position to win in November”, she said.

Each side had gains and setbacks in the overall struggle for control of Congress.

The Republican establishment lost a battle in Arizona, and, if its calculation is right, possibly a House of Representatives seat, too.

Randy Graf, a conservative who made illegal immigration a centrepiece of his campaign, won a primary to succeed retiring Republican Rep. Jim Kolbe. He defeated Steve Huffman, who had the support of Kolbe and the Republican congressional campaign committee, which financed television campaigns in the final days of the race.

Democrats, who need to gain 15 seats to win control of the 435-member House, had run ads attacking Huffman in hopes that Graf would win the primary. Their calculation was the same as Republican strategists — that Graf is too conservative to carry the district in November. The Democratic candidate is Gabrielle Giffords, who easily won her party’s nomination.