Russia has long insisted on a solution of the conflict which removes the root causes of it. It can not allow for Ukraine to become a NATO battering ram at its doorstep. It can not allow a fascist government in Ukraine.

Any solution to the conflict must resolve (at least) those two issues.

The Trump administration wants the Ukraine problem out of its way. It wants to implement a ceasefire to be able to turn away and ignore the festering problem.

Russia won't have that (archived):

On Tuesday, Moscow reinforced its hard-line, maximalist demands when Russia's Deputy Foreign Minister Sergei Ryabkov complained that Russia's demand "to solve the problems related to the root causes of the conflict" was being ignored by the U.S., and "we cannot accept all of this as it is."

As the U.S. overstates its progress in talks, Moscow seems concerned that Trump's negotiators do not understand how serious it is about these demands, according to [Thomas Graham, senior director for Russia at the National Security Council under the George W. Bush administration and now a fellow at the Council on Foreign Relations].

"The question is whether the administration has the patience to continue those negotiations and whether they can conduct the negotiations in ways that can extract concessions from the Russian side," he said.

"Extract concessions"? By what?

The U.S. has no leverage over Russia. It is the Russian army that is winning on the battlefield in Ukraine. It has ample reserves in soldiers. It is by far outproducing NATO in weapons and munitions. It is stable in political, social and economic terms.

Secretary of State Marco Rubio is threatening Russia with more sanctions (machine translation):

"Now we are not interested in negotiations for the sake of the negotiations themselves – we will not continue this indefinitely. We have a certain amount of time during which we want to understand whether they are ready or not, and this time is already coming to an end. Congress has already started working on a bill for additional sanctions, and pressure from the Capitol will continue to grow, " the US Secretary of State said.