Maine Sen. Susan Collins decried the influence of “dark money” in political campaigns and outlined issues on which she has supported and opposed President Trump during a wide-ranging interview on public radio Friday.

Collins, appearing on Maine Public’s “Maine Calling” radio show, did not announce whether she would run for re-election, but said she would make a decision this fall.

The 2020 U.S. Senate race in Maine is expected to be hotly contested, and has already attracted outside groups trying to unseat Collins, a Republican who has held the seat since 1997.

One of the groups is the 16 Counties Coalition, headed by veteran Democratic staffers and campaigners. Leaders of the group refused to disclose donors or spending plans for the 2020 campaign when asked by the Press Herald in July.

A 2010 U.S. Supreme Court decision, Citizens United, shields “dark money” groups from having to disclose donors.

“I’ve never had so much money spent against me in negative ads so early,” Collins said on the radio show Friday. “People should know where this money is coming from. I would support a bill to require all groups to disclose their donors.”

Collins cast a key vote against the DISCLOSE Act – it failed by one vote in the Senate in 2010 – which would have required disclosure of donors, but carved out exemptions for the National Rifle Association and other groups. Some analysts argued that labor unions were favored in the DISCLOSE Act. No Republican senators supported the DISCLOSE Act, and only two Republicans in the House voted with Democrats for the bill.

Collins said she voted no because there were too many exemptions granted to special interest groups.

Marie Follayttar, a leader of liberal activist group Mainers for Accountable Leadership, said Collins is part of the reason why “dark money” in political campaigns is so prevalent. She said the DISCLOSE Act was not perfect, but would have been a step in the right direction.

“It’s disingenuous for Susan Collins to complain about dark money when she has served 22 years in the Senate, and not only voted against the DISCLOSE Act, but also didn’t bring forth her own initiatives to combat dark money,” Follayttar said.

Collins supported the McCain-Feingold campaign finance reform bill in 2002, but large portions were repealed because of the Citizens United decision.

Collins said she believes both the “far right” and the “far left” have too much influence on the Republican and Democratic parties.

“My hope is both parties can get back to the middle,” Collins said. “The middle is where most Americans are.”

Democrats, including House Speaker Sara Gideon, liberal activist Betsy Sweet and Saco attorney Bre Kidman, are lining up for a chance to take on Collins.

Collins praised Trump for cutting taxes, but criticized him for moving to divert money approved by Congress for other purposes to pay for building a border wall. Collins pointed out that the Constitution gives “purse strings” powers to Congress.

“The president in my judgment is not acting in accordance with the separation of powers laid out by our Founders, by (being in favor of) diverting billions of dollars allocated from one purpose to another,” Collins said. National news reports have detailed how the Trump administration plans to divert billions in defense spending and Federal Emergency Management Agency money for border wall construction.

Collins did not endorse Trump in the 2016 general election, and she has not said whether she would support the president in 2020.