They didn't full-out invade

Correct, they were repelled from the beaches by Socialists

Putting American boots on the ground is not the only way that the United States brings death and destruction to a region to further (or protect, as some Amercan politicians call it) American, and more broadly western, hegemony (or American interests, as craven ghouls call it). The use of proxy forces like in Afghanistan during the 80s, coups like those carried out in Chile in 73 and, well really most of South America in the latter 20th century, sanctions against countries like Cuba, Venezuela, and the DPRK (which are explicitly put in place to make life worse for the people living there and produce people who would be willing to commit violent acts to overthrow the local government not adequately subordinate to the United States), facilitating the mass murder of people opposed to the pro-america regime or too supportive of communism like in Indonesia and South Korea several times, all bring massive loss of life and terrible suffering. The crimes against humanity carried out by the United States and on their behalf are so terrible and widespread that it is difficult to name a country that has not had blood spilled to advance American hegemony in it. Like Cuba.

At that though, the United States is no stranger to directly deploying troops to crush opposition to American hegemony. Like in Vietnam, Korea, Afghanistan again, and the RSFSR immediately after the revolution. War is terrible, but it is not out of the question to enforce American hegemony.

In Ukraine, the United States is not interested in preserving democracy or the self determination of the Ukranian people. It never has been in any of the countries or among any of the organizations that receive its support. The United States ultimately wants to have control over the Russian economy to use as a source of cheap labor and resources. That was the USSR and later Russia were denied, several times, entry into NATO, an ostensibly defensive alliance for the region that Russia is in, and the purpose of the rapid privatization of post-soviet economies after '91. Ukraine is caught in the terrible position of being used to advance the United States' goal in the region. Support for Ukraine will be dropped when the United States government believes that it is no longer useful or viable to support them against Russia, after who knows how many people are dead and permanently injured, and how many more whose entire lives have been destroyed.