The problem with any GOP contenders thinking they will challenge Trump in 2020 is that, barring something disastrous, he will run and will not lose his base support.
Thus, any GOP contender who might somehow win the nomination would likely lose most of the support that would have gone to Trump [again]. A GOP contender would be handing the election to the Democrat, assuming they don’t nominate a nutcase.
I think the GOPe plan is exactly that - nominate some establishment candidate that will most likely lose to the Democrat because most conservatives will feel alienated. And even if the establishment Republican wins, he will do what the Uniparty wants pretty much like the Democrat would have done, so all the crony capitalists and oligarchs will be rewarded either way.