Donald Trump dropped some of the US’s tariffs on Canada on Friday to “better serve the public interest” the White House said, handing a win to Susan Collins, the embattled Republican senator for Maine, as she faces a tight re-election campaign that will help determine whether Democrats can flip control of Congress.

Collins announced that several industries the exemptions would apply to nine agricultural products, including blueberries, potatoes, apples and seaweed. She added that many of the state’s farmers rely on specialized equipment and materials from across the border that are “unavailable from American suppliers or cannot be replaced without incurring significant expense”.

“In my repeated conversations with Ambassador Greer, Secretary Lutnick, and other senior administration officials, I have asked for tariff relief for these important products, and I will continue working directly with administration officials to seek additional relief and encourage a broader trade agreement with Canada, our neighbor, ally, and largest trading partner,” she wrote.

The White House also specified that certain processing equipment – such as plywood sheets, packing boxes, paper products, and certain machinery – would be removed from its tariffs. These materials can be crucial for Maine businesses operating close to the border.

“President Trump is further refining the scope of the July 20 and September 8 actions to better serve the public interest, and to ensure these measures continue to effectively offset the burden or disadvantage to US commerce from Canada’s discriminatory measures,” the White House said in a news release.

Collins, who has served in the Senate for nearly 30 years, is running for re-election against Troy Jackson, a Democrat who has served in the Maine state senate and was a former logger. The race is crucial for the Democratic party’s hopes of flipping control of the chamber, and is so far considered a toss-up.

The trade war between Canada and Maine has touched a nerve in the state, which relies heavily on trade with Canada. Many of the industries most entrenched in the state’s history – such as logging, lobstering and fishing – were expected to take a hit after Trump’s tariff announcements this year.

Earlier this week, Canadian prime minister Mark Carney said American tariffs hurt both American and Canadian households. He added that auto exports to the US have so far fallen 10%, and US exports to Canada have fallen by more than 20%.

“US tariffs have upended a trade bargain that’s existed for decades,” Carney said. “They’ve raised costs for American families while putting Ontario workers and businesses at a disadvantage and under a cloud of uncertainty.”

After Trump placed a 50% tariff on certain Canadian goods, which began 22 August, Canada announced its own retaliatory tariffs in response, ranging from 15% to 50% on $20bn worth of American goods. Canada later withdrew its tariffs on American seafood, which helped Maine’s fisheries in particular.

Maine is considered a purple state, and many within the state – including Collins – consider themselves to have an independent streak. Collins has frequently sought to distance herself from Trump, particularly when it comes to his trade policies, and has broken with her party more than any other Republican senator since Trump took office, according to a New York Times analysis of her voting record.

But her efforts to vote against Trump’s policies have rarely succeeded in his second term so far, the analysis found.

Jackson has frequently seized on this line of attack since replacing Graham Platner on the Democratic ticket. At a television debate earlier this month, Jackson also pointed to Collins’s crucial vote to confirm conservative supreme court justice Brett Kavanaugh. The court subsequently overturned Roe v Wade.

“Tonight is about who you stand with when it matters,” Jackson said in his opening statement.

Democrats argued the decision to drop some Canadian tariffs was an admission by the White House that Trump’s policies were unpopular.

Ron Wyden, the top Democrat on the Senate finance committee, called the move a “desperate, 11th hour attempt to save Susan Collins’ political career”.

“The only way to get Trump to reverse course,” he said, “is for Americans to send a message that his sabotage of the American economy has got to go, along with any politician who has supported his agenda.”