Poliquin was defeated by Democrat Jared Golden in his 2018 run for reelection; he became the first incumbent to lose his seat in Maine's second congressional district since 1916.

Poliquin claimed the ranked-choice voting process used in the election was unconstitutional and declared himself the winner because he led after the initial tally.

Dale McCormick, the authority's director and an appointee of Democratic governor John Baldacci, approved the proposal following a reduction in the per unit price to $265,000.

Maine Attorney General William Schneider advised Poliquin to disassociate himself from his business ventures but did not offer an opinion as to whether he had actually violated the Constitution.

A 2009 Maine Forest Service report discussed Poliquin's property as an example of one that might not be fully complying with the law, stating that restrictions on timber harvesting in shoreland areas would limit any commercial use of the land.

[23] In the general election Poliquin faced Democratic nominee Jared Golden and independent candidates Tiffany Bond and Will Hoar.

Maine Secretary of State Matt Dunlap called the claims "a distraction" and cautioned the campaign to avoid "irresponsible" attempts to slow down the tabulation process and erode faith in the system.

[32] In the Republican primary, he defeated Liz Caruso,[33] a wilderness guide and local government leader from the village of Caratunk, who raised $37,000 to Poliquin’s $2.2 million.

[35] Some political analysts thought Poliquin could win the general election, but he consistently trailed in the polls and lost to Golden, 53%–47%, after the ranked-choice tabulation.

[41] In April 2016 Poliquin and Chellie Pingree (ME-1) proposed legislation that would allow Cuban-bound flights to make technical stops at American airports for refueling and restocking.

[42] Poliquin and Niki Tsongas (MA-3) pushed legislative efforts begun during the tenure of his Democratic predecessor, Mike Michaud, to require the U.S. Department of Defense to purchase U.S.-made sneakers.

He called for congressional hearings in the region where the proposed park is now, and said federal officials and non-local supporters ignored the concerns of local residents who opposed it.

[44] Poliquin was a member of the Republican Main Street Partnership[45] and the United States Congressional International Conservation Caucus.

[46] In November 2017 Poliquin said he would vote for the new Republican tax bill, whose framers had dismissed "a late suggestion by President Donald Trump to lower the top rate on high-wage earners."

"We want to eliminate as many of these loopholes and special-interest carve-outs that only the wealthy and well-connected are able to take advantage of," he said, describing the work on the bill as "very methodical, very transparent and very thoughtful."

Noting that he had voted earlier in November "to move the tax proposal forward in the House, trusting the Senate would continue to work on it and improve it," he expressed approval of the changes Senator Susan Collins and others made "that will benefit Maine families and small businesses, such as retaining the medical expense deduction and improving the provision dealing with historic tax credits.

"[48][49] In December 2017 the International Trade Commission ruled 4–0 to activate tariffs on Chinese hardwood plywood, thus leveling the playing field for U.S. wood products, a decision Poliquin had urged upon them at an October hearing.

The Democratic Leader of the Maine State Senate, Troy Jackson (D-Allagash), praised Poliquin "for his successful efforts to fight against illegal and unfair foreign trade".

"[50] On February 3, 2015, Poliquin was one of three House Republicans to vote against repealing the Patient Protection and Affordable Care Act, commonly known as Obamacare.

[51] His spokesman said that while Poliquin supported repeal, the proposed bill did not offer a "free-market alternative" to immediately take its place, which he felt was needed.

[52] Poliquin was subsequently criticized by conservative groups seeking immediate repeal of the law, including the Republican Liberty Caucus, which voted on February 5, 2015, to rescind their endorsement of him.

"[67] In May 2016, Poliquin voted against a measure intended to uphold an executive order that barred discrimination against LGBT employees by religious organizations that contract with the federal government.

[68] In 2016, Poliquin drafted a bill that would prohibit the federal government from giving food stamps to individuals convicted of terrorism-related crimes.

"[70] On February 11, 1992, Poliquin's wife, Jane, drowned in a swimming accident at the Palmas del Mar Beach Resort in Humacao, Puerto Rico.