AUGUSTA — David Costello announced Wednesday that he will seek the Democratic nomination to take on Republican U.S. Sen. Susan Collins next year.

Costello, who ran unsuccessfully last year as a Democrat against independent Gov. Angus King, said he’s running to “end the Trump Administration’s and Republican Congress’s reckless assault on our democracy, environment, and economy.”

“Senator Collins, aside from expressing concern, has done little to prevent the Trump Administration and her Republican colleagues from undermining our economy, our critical government programs, and our nation’s long-standing defense of democracy against authoritarianism and aggression,” Costello said in a written statement.

Collins chairs the powerful Senate Appropriations Committee and has used her influence to push back and in some cases reverse unilateral funding and program cuts by the Trump administration, which she has described as “illegal,” since it’s being done without congressional approval.

Collins also has a split record on Trump’s most controversial Cabinet members. She voted against Pete Hegseth as defense secretary and Kash Patel as FBI director, but supported Tulsi Gabbard as director of national intelligence and vaccine-opponent Robert F. Kennedy Jr. as secretary of the Department of Health and Human Services.

Democrats believe Collins is vulnerable this year. She’s the only Republican running in a state won by Vice President Kamala Harris won in November. But recent polling has shown her approval rating on the rise, and Collins has defied the odds before.

The 65-year-old Brunswick resident is the third Democrat to formally declare against Collins, who is seeking a sixth, six-year term in the Senate.

Jordan Wood, a 35-year-old Bristol resident, declared his candidacy in April and has been holding town hall events across the state. Wood is a former chief of staff for U.S. Rep. Katie Porter, D-Calif., and founder of democracyFIRST, a Democratic Super PAC.

Natasha Alcala has also declared a run. She also filed paperwork to challenge King last year, but never qualified for the ballot.

Gov. Janet Mills, meanwhile, has been facing pressure from national party leaders to take on Collins, especially after her high-profile clash with President Trump at the White House over transgender student athletes, which has been used to raise money. Mills says she’s neither planning to run, nor has she ruled it out.

And House Speaker Ryan Fecteau, D-Biddeford, is also considering a run, though he is currently trying to wrap up the legislative session, which is scheduled to end next Wednesday.

Other candidates who have filed paperwork with the Federal Election Commission include independent Phillip Rench and Republicans Carmen Calabrese and Daniel Smeriglio.

Costello has decades of experience in government, but his candidacy against King, who routinely tops the polls as Maine’s most popular politician, never caught traction with Democrats.

Costello placed third with about 11% of the vote, behind King, who received 52%, and Republican Demi Kouzounas, who received 36%.

“In 2024, I campaigned to strengthen our democracy and bolster the federal government’s ability to address such pressing challenges as climate change, lack of affordable housing and health care, economic inequality, and insufficient retirement security,” he said. “These are challenges the Trump administration and Sen. Collins and her Republican colleagues are either ignoring, or worse yet, exacerbating.”

In a news release, Costello said his work experience includes having held a high-level position at US AID, where he managed foreign aid in Cambodia, Haiti, Bosnia, Serbia and Kosovo. He has also worked as a senior aide to the Maine secretary of state, the mayor of Baltimore and the governor of Maryland, as well as deputy and acting secretary of the Maryland Department of the Environment.