Depends when you want your POD. Pre WWII, I like the idea of a Soviet victory in the Polish war and a surviving Weimar state.
Post-WWII, I'd suggest no Marshall Plan for starters, with a nice continuation of Truman's drawdown of the American military, coupled with no Korean War and some sort of distraction in the Western Hemisphere or Asia. Maybe even have the Soviet Union play the diplomatic game smart and recognize the Monroe Doctrine with a treaty, in order to appease the isolationists you'd have to have in order for this scenario to succeed.
Anyway, here's how I'd have it play out. Get Taft elected President in 1948. He's one of the last staunch isolationists, and he'll do the job in getting rid of the Marshall Plan, and he won't go through with NATO. Have the Soviet Union recognize the United States's control of the Western Hemisphere, and back that with the Soviet Bomb in 1949. Hopefully, the Soviet declaration will bank the fires of the Red Panic, and you won't have that fuelling American desires for intervention.
Let's say Taft becomes embroiledi in domestic issues, and indeed does well, even moving the United States slightly to the left with farm subsidies, federal financial aid, and a lot of the other stuff he did in OTL, and probably would've continued in TTL. But foreign issues are another matter entirely, and the Taft administration fumbles those badly. The Cuban situation continues to deteriorate, but Taft is reelected for a second term in 1952, and continues his policies of isolationism, domestic liberalism, and military cuts. These result in an earlier Civil Rights movement, but almost eliminate the U.S. military, which sees its numbers slashed to 1930s levels, with the notable exception of nuclear weapons, which Taft publicly and repeatedly states are to defend the neutrality and peacefullness of the United States.
The Soviet Union, meanwhile, continues much the same as OTL, but Beria succeeds Stalin, and continues the Stalinist terror and secretly prepares for the neutralization of Western Europe, which he misguidedly views as a threat. In TTL, without the help of the United States, Europe will lean much, much more to the left, with Greece, France, Italy, and likely a few other nations going completely Communist. Spain, Britain, Portugal, and a few others will definitely not. Depends on how you want the story to go.
In the late 1950s and early 1960s, Taft's predecessor faces problems in Cuba, where rebels have overthrown the Batista government. He rushes troops to assist, but the badly-equipped American troops take heavy losses and are pushed back. This is TTL's Vietnam. It can last as long as the story dictates, but the end result is a badly bloodied United States that, after 16 years of isolationist Presidents and Congresses, and one Cuban War later, has a dread of foreign entanglements equal to or greater than OTL's 1930s United States.
This should set the table for you, Chris.