Sen. Susan Collins, who did not support President Trump during the 2016 election, has refused to say how she voted on this year’s presidential primary ballot.

Collins’ campaign spokesman Kevin Kelley declined to answer questions about the matter Sunday or Monday and instead referred the Press Herald to an interview the Republican senator did last Friday with NewsCenter Maine.

At the close of the 6-minute segment, reporter Pat Callaghan asked Collins if she would be voting in the presidential primary this year and whether she will be supporting the president or writing in someone else, as she did four years ago.

Collins said she already voted by absentee but would not reveal her vote, pointing out that others have not done so.

“I would note that it’s on the Democratic side that there are eight candidates, and my likely opponent, as well as the governor and many other Democratic officials have not said who they are going to choose in what is a contested Democratic ballot,” she said. “I’m focused on my job and also on my own campaign and I’m just not going to get involved in presidential politics.”

Since Trump is the only Republican on the Maine primary ballot, she either voted for him, wrote in another name or left the question blank.

Collins, who was first elected to the Senate in 1996 and has been reelected three times since with increasing support each time, likely faces her toughest challenge yet.

She will face the winner of a Democrat primary between Maine House Speaker Sara Gideon of Freeport, progressive activist and lobbyist Betsy Sweet of Hallowell, former Google executive Ross LaJeunesse of Biddeford and defense attorney Bre Kidman of Saco.

Gideon said in a statement Monday that she is still making her decision on whom to support for president. LaJeunesse indicated that he would support whoever wins the Democratic nomination. Sweet announced Sunday that she was supporting U.S. Sen. Bernie Sanders of Vermont. Kidman did not respond to questions from the Press Herald.

Collins’ decision to not reveal how she voted speaks to the challenges she faces seeking re-election to a fifth Senate term.

If she says she voted for Trump, it’s another negative in the eyes of independents and even moderate Democrats who may have supported her in the past but now see her as beholden to Trump. Her vote to confirm controversial U.S. Supreme Court nominee Brett Kavanaugh and her vote to acquit Trump during his Senate impeachment trial already have earned her scorn among some who were counting on her to buck her party.

If she says she did not vote for the president, she risks angering the Republican Party base, which is enthusiastically pro-Trump.

In August 2016, as many high-profile Republicans wrestled over whether to support the former New York real estate developer-turned-reality TV host as nominee, Collins penned an op-ed saying she could not.

“This is not a decision I make lightly, for I am a lifelong Republican. … But Donald Trump does not reflect historical Republican values nor the inclusive approach to governing that is critical to healing the divisions in our country,” she wrote.

“My conclusion about Mr. Trump’s unsuitability for office is based on his disregard for the precept of treating others with respect, an idea that should transcend politics. Instead, he opts to mock the vulnerable and inflame prejudices by attacking ethnic and religious minorities.”

Collins later said she wrote in former House Speaker Paul Ryan.

Although many Republican members of Congress have actively courted the president’s support, Collins has not.

In December, however, her Senate colleague, Lindsay Graham of South Carolina, tweeted that Collins “showed unbelievable courage” during Kavanaugh’s confirmation hearing and must be reelected. Trump retweeted Graham, adding “I agree 100%!”

A Colby College poll last month of slightly more than 1,000 Maine voters showed Collins and her leading Democratic challenger, Gideon, with virtually identical support nine months before Election Day.

The survey was conducted Feb. 10-13 and asked voters whom they would choose between Collins and Gideon. Gideon led narrowly with 43 percent support, compared to 42 percent for Collins, with 14 percent undecided.

Independents Tiffany Bond, Danielle VanHelsing, Linda Wooten and Lisa Savage also are competing.