That's absurd. Churchill was a conservative? Yes. An imperialist? Yes. A racist? Yes. But you cannot compare him to Iosif Stalin, a totalitarian dictator who caused millions of deaths. Churchill was a human being, with his defects, but he was a supporter of democracy and freedom, Stalin was a monster.
Winston Churchill held strong imperialist ideas and held some racism too, as the majority of his time's people, but his nationalism was deeply rooted in his affection to British Empire, so living in United States could change that.
So a interventionist President who loves free trade, leads US against authoritarianism and is pretty racist? That seems more Woodrow Wilson then Stalin, in fact Wilson was widely more an unabashed racist then Churchill as Wilson allied himself with KKK and other suprematist organizations while Churchill hated Nazis.
So Churchill grows in America and enters in politics as Democrat because he disagrees with Teddy Roosevelt's economic policies, although his support for "Big Stick" doctrine. Then he leaves the party for protest against Wilson's neutralist line and his strong campaigning is enough to narrowly swing California, giving Charles Evans Hughes the Presidency in 1916.
Wilson makes a comeback in 1920 and is elected due Hughes's unpopularity for the war, the he dies in office and is succeeded by his Veep (for example James Cox), who stay until 1933. The Twenties are a Democratic decade.
Then the 1929 Crash changes the situation and in 1932 a Republican, possibly progressive, is elected, maybe Borah. He gives the Vicepresidency to Churchill to balance the ticket with right wing of the party. Borah supports the Appeasement with Hitler, for great disappointment of Churchill, but dies in 1940, allowing Winnie to take the power. He leads US to victory during Second World War, after British surrender. He is defeated for a third term in 1948, while he plans to start a preventive attack to Soviet Union, but makes a comeback in 1952 before retiring four years later, as the lone President to serve more then two terms.
28 Thomas Woodrow Wilson (D-New Jersey)/ Thomas Reilly Marshall (D-Indiana) 1913-1917
29 Charles Evans Hughes (R-New York)/ Charles Warren Fairbanks (R-Indiana) 1917-1918
Charles Evans Hughes (R-New York)/ Vacant 1918-1921
30 Thomas Woodrow Wilson (D-New Jersey)/ James Middleton Cox (D-Ohio) 1921-1924 [Died in Office]
31 James Middleton Cox (D-Ohio)/ Vacant 1924-1925
James Middleton Cox (D-Ohio)/ John William Davis (D-West Virginia) 1925-1933
32 William Edgar Borah (R-Idaho)/ Winston Leonard Spencer Churchill (R-New York) 1933-1940 [Died in Office]
33 Winston Leonard Spencer Churchill (R-New York)/ Vacant 1940-1941
Winston Leonard Spencer Churchill (R-New York)/ Wendell Lewis Wilkie (D-Indiana) [National Union Ticket] 1941-1944
Winston Leonard Spencer Churchill (R-New York)/ Vacant 1944-1945
Winston Leonard Spender Churchill (R-New York)/ Earl Warren (R-California) 1945-1949
34 Scott Lucas (D-Illinois)/ Harry Truman (D-Missouri) 1949-1953
35 Winston Leonard Spencer Churchill (R-New York)/ Richard Milhous Nixon (R-California) 1953-1957