MILLINOCKET, Maine — The man who led a successful campaign for the creation of a national monument on land his family gave to the federal government in the Katahdin region now plans to run for Congress.

Democrat Lucas St. Clair will announce his candidacy for Maine’s 2nd Congressional District at the Appalachian Trail Cafe in Millinocket on Monday.

The venue highlighted his family’s donation of 87,562 acres that is now Katahdin Woods and Waters National Monument.

If he tops a June Democratic primary field that currently includes four others, St. Clair would go on to challenge Republican U.S. Rep. Bruce Poliquin.

Poliquin has advocated aggressively against the national monument designation.

St. Clair, the 39-year-old son of Burt’s Bees entrepreneur Roxanne Quimby, has never held elected office. He will file his candidacy paperwork with the state and launch his campaign website Monday, said his spokesman, David Farmer.

Assistant Maine House Majority Leader Jared Golden of Lewiston is the likely Democratic frontrunner to challenge Poliquin in a congressional district that has seen voters increasingly switch allegiances to Republicans, including Poliquin in 2014, Donald Trump in 2016 and a clear majority of legislative races.

A resident of Lewiston, a Democratic Party stronghold, the 34-year-old Golden is a Marine veteran who served in Afghanistan and Iraq and has been highly visible on veterans’ issues in Augusta. They’re a key constituency in the 2nd District and Poliquin sits on the House Veterans Affairs Committee.

The monument would likely be a theme in the race if St. Clair stays in it, though other issues with a wider impact on Maine will round out the debate. Poliquin is the only Republican representative from New England, and he has drawn criticism for voting in May for a House bill to replace the Affordable Care Act, which a Kaiser Family Foundation analysis said would raise health insurance premiums disproportionately for Maine’s older rural residents.

St. Clair lives in Portland but plans to move to Hampden. He said he believes that his experience running the campaign that persuaded then-President Barack Obama to designate Katahdin Woods and Waters in August 2016 — with help from a $40 million endowment pledged to support the monument — gave him valuable insight into the lives of the northern Mainers he would represent. He stays involved with the monument as president of its advocacy group, Friends of Katahdin Woods and Waters.

Poliquin, a former state treasurer, is serving his second term in Congress. He first won the seat, which had been in Democratic hands for two decades, in 2014 as an underdog against Democrat Emily Cain of Orono. Whoever wins the Democratic primary will face a daunting challenge: In the past century, no incumbent has lost the seat in an election.

St. Clair also faces opposition from Democrat Jonathan Fulford of Monroe, a carpenter and plumber who twice ran unsuccessfully for the Maine Senate seat currently held by Senate President Mike Thibodeau, a Republican from Winterport. Two other Democrats, Philip Cleaves Jr. and Timothy Rich, have already entered the race.

U.S. Secretary of the Interior Ryan Zinke (left) laughs with Lucas St. Clair during a tour of the Katahdin Woods and Waters National Monument, June 14, 2017.