Republican Governor John Kasich of Ohio, a staunch opponent of President Donald Trump, is reportedly considering a plan to challenge Trump in 2020 as part of a “unity” presidential ticket with Democratic Governor John Hickenlooper of Colorado.

Under the plan, both Kasich and Hickenlooper would leave their respective parties and run as independents with Kasich at the top of the ticket, according to sources who spoke with Axios; the sources cautioned the idea of a “unity” ticket has only been casually talked about.

“The idea of a joint ticket has been discussed, but not at an organizational or planning level,” said the source. “What they are trying to show the country is that honorable people can disagree, but you can still problem solve together. It happens in businesses and it happens in families. Why can’t it happen in Washington?”

Hickenlooper and Kasich have been holding joint press conferences to discuss their healthcare proposal, and will reportedly expand their platform to include immigration and job creation. They are also in talks with “major media companies” about a possible podcast or cable show.

“Watch on the policy front as they expand beyond healthcare and also include other governors into the coalition,” added the anonymous source.

For his part, Hickenlooper has refused to rule out running alongside Kasich, telling Politico earlier this month “I don’t think it’s in the cards. But I do like the idea of working with him in some context at some point.”

Kasich has made no secret of his dislike of President Trump following his defeat in the Republican presidential primary in 2016. Despite public statements indicated he will not run against Trump, sources close to Kasich told NBC’s Willie Geist there is a growing sense of “moral imperative” to run in 2020.

Moderate Republicans are already publicly speculating about a challenge to President Trump in 2020, with Arizona Senator Jeff Flake suggesting Trump is “inviting” a primary challenge.

“I think he could govern in a way that he wouldn’t,” he said in an interview with Georgia Public Broadcasting. “But, I think that the way that — the direction he’s headed right now, just kind of drilling down on the base rather than trying to expand the base — I think he’s inviting [a challenge].”

Maine Senator Susan Collins said “It’s too difficult to say,” whether or not Trump will be the Republican nominee in 2020.