According to White House Press Secretary Sean Spicer, President Trump “expects” Russia to both make the level of violence in Eastern Ukraine go down, and to unconditionally “return” the Crimean Peninsula to the Ukrainian government, adding that he “also expects to get along with Russia.”
After protests in Kiev ousted the pro-Russian government in Ukraine, the Autonomous Republic of Crimea held a referendum on secession from the Ukraine in March 2014. A region dominated by ethnic Russians and host to a major Russian military base, that referendum easily passed, and Crimea sought and received accession into the Russian Federation days later.
The post-revolution Ukraine government was pro-West, and naturally Western nations rejected the Crimean secession as unlawful, accusing Russia of “annexing Crimea” militarily. Despite this claim, no real military action ever took place, and the only movement of forces came after the referendum, when Ukraine managed to borrow enough gasoline and car batteries to get their military vehicles off the peninsula.
The US has vowed never to accept Crimea as part of Russia, however, and has repeatedly demanded Russia unconditionally “return” Crimea. Clearly Russia has no intention of doing so, and threats aside Ukraine has no practical way to expel Russia from the peninsula.