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CNN —  

Sara Gideon, Maine’s Speaker of the House, announced on Monday a campaign against Sen. Susan Collins, attempting to replace her potential opponent’s independent image with one connected to less popular Republicans like President Donald Trump.

In her campaign video, Gideon, a Democrat, made clear that her candidacy would focus on economic and health care issues, from protecting the Affordable Care Act to controlling the costs of prescription drugs.

But she also attacked Collins for not taking on Republican leaders, saying she did when she overcame a veto from former Gov. Paul LePage to expand access to an opioid overdose treatment. Gideon showed clips of Trump and Senate Majority Leader Mitch McConnell praising Collins, even though she has not always reciprocated. Collins, who opposed Trump in 2016, has not said whether she’d endorse him in 2020.

“Getting things done for Mainers is what we’re elected to do, not falling in line behind the demands of someone else,” said Gideon in her video. “It doesn’t matter if that person is Paul LePage, Mitch McConnell or Donald Trump.”

Collins, who has served in the Senate since 1997, is the only Republican in Congress from any of the six New England states. She’s been able to succeed where other Republicans have failed by burnishing her bipartisan credentials and has thrived even in tough election cycles for her party. In 2008, she dominated her re-election race against then-Rep. Tom Allen as Barack Obama thumped John McCain in Maine.

But it is expected to be more difficult for Collins in the Trump era. In the past couple of years, she’s proven her power as the deciding vote on some of the most consequential issues in Washington, lifting and depressing the spirits of both liberals and conservatives at various critical moments.

In 2017, Collins, the late Sen. John McCain of Arizona and Sen. Lisa Murkowski of Alaska stopped a GOP bill that would’ve decimated the ACA. A few months later, Collins supported the Republicans’ tax overhaul bill, which provided benefits for individuals but even more so for corporations and business owners.

Collins also supported many but not all of the conservative judicial nominees put forward in the Senate and served as a crucial vote for Supreme Court Justice Brett Kavanaugh.

Republicans say Collins will secure a fifth term since she is one of the few senators left who is still willing to put her constituents’ priorities over her party’s, and a spokesman for Collins pointed to her seniority as an attribute Maine’s voters value in her.

“One of the reasons why Senator Collins has been so effective is that she has more seniority than any U.S. Senator from Maine over the past 70 years,” said Kevin Kelley, a spokesman for Collins, in a statement. “She will continue to build on her record of extraordinary accomplishments for the people of Maine.”

Collins said Monday evening on Capitol Hill she will formally announce her candidacy this fall.

“There are two opponents in the Democratic primary, so my opponent won’t be decided until next June,” Collins told reporters in the Capitol. “I always take any opponents seriously.”

Sen. Todd Young, an Indiana Republican who chairs the National Republican Senatorial Committee, said he is confident Collins will be reelected.

“Susan Collins is one of the most bipartisan senators we’ve seen around this place in a long time,” Young said. “She’s a great fit for the state of Maine and no one is more respected among her colleagues. She’s prepared for whoever come her way and she will earn reelection.”

This story has been updated with additional developments.

CNN’s Ted Barrett and Manu Raju contributed to this report.