Sen. Susan Collins of Maine joined CNN’s “State of the Union” on Sunday morning where she said she sees “nothing wrong” with Republicans challenging the president in the 2020 primaries. “It’s always interesting when we have primaries because a lot of times it allows different viewpoints to surface,” Collins said. “It can help influence public policy down the road and it’s healthy for our democracy.”

Collins didn’t say whether she would endorse Trump for president in 2020, adding that she would wait until then to discuss the election. “That is a lifetime in politics,” she said.

With the 2020 cycle just around the corner, some Republicans have floated potential runs to challenge Trump, and the anti-Trump conservative movement has called for more opposition to the president.

Some anti-Trump conservatives attended a conference just last week to assess how the center-right can move forward post-Trump, the New Yorker reported. Larry Hogan, the Republican governor who was re-elected this November in Maryland spoke at the conference.

Conservative commentator George Will left the GOP in 2016 over Trump’s candidacy and has urged other Republicans to do the same. “This is not my party,” Will said at the time. Earlier this year, he admonished the party for continuing to support Trump in the upcoming presidential election.

Outgoing Ohio Gov. John Kasich said last month that he was “very seriously” considering a run against Trump. Kasich said he was concerned about Trump’s name-calling and growing divisions across the country, and also took issue with the administration’s policies.

Republican Sen. Jeff Flake of Arizona said earlier this year that he also hopes “somebody else runs in the Republican primary,” Politico reported. He said he wouldn’t rule out running himself, but added, “I need a break.”

Even as some in the GOP consider opposition to Trump, a recent Gallup poll found that nearly 90% of Republicans think the president has done a good job so far.

As for Collins, she told CNN’s Jake Tapper that anyone who opposes Trump in the primaries would “probably have an uphill climb,” and expressed concern that Congress is “getting into this perpetual campaign mode instead of focusing on governing.”