Hmm. (I'll note upfront I don't know enough about Russian politics, so my focus is aimed at a US in decline. Hopefully someone else can handle a better Russia—I give them Korea and tighter ties/control of Communist China.)
Chiang Kai-shek conducts the post-WWII civil war better, bottling up Communist forces in Manchuria and leaving them to rot while embarking on domestic reforms to boost popularity.
However this works only somewhat better than OTL and results in a more even battle between Communists and Nationalists, with higher popularity for the Nationalists meaning the ChiComms really are heavily supplied by the USSR in the ATL in order to keep moving forward.
This brings increasing American forces into the fighting, culminating in the commitment of ground troops in Korea to keep it free.
Although this means Korea remains united and non-communist the USSR is perturbed and throws more support behind the ChiComms.
The earlier Nationalist popularity begins to fade and Communist forces stage a series of successful attacks along the coast. American naval forces are redeployed directly into the action and the American occupation of Japan deepens as more and more basing is required.
Meanwhile in Europe the Marshall Plan is noticeably more niggardly than OTL as American resources have been thrown into East Asia.
Taft beats Dewey at the '48 convention (and then accepts Governor Warren of California as his running mate), and goes on to narrowly defeat Truman in the general election. This results in pull-back of American forces from East Asia which leads to a series of Communist victories over the Nationalists. (The Marshall Plan is also abandoned.)
Over the next few years the Nationalists are forced back to Taiwan while American forces abandon the occupation of Japan and pull out of Korea.
Russian forces preempt their ChiComm allies and roll into Korea on a pretext that the "Allies" have to maintain order.
In America Taft works hard to curb domestic spending combining program reduction with a mixture of tax cuts in an overall attempt to strongly reduce public debt and set the United States on a solid balanced budget keel. He does, however, support certain "liberal" programs such as public housing & Social Security. Notably his strong civil liberties stance adds a number of laws to the books of the United States preventing the use of SS numbers for any use besides Social Security itself. Finally his elimination of many farm subsidies saw a number of farm states go Democratic in '52—this was counterbalanced by Taft winning several Southern states.
Taft wins the '52 general election against Democratic Governor Adlai Stevenson (and his running mate, Senator Kefauver) but his victory is short-lived—he steps down as President in '53 when he discovers he has terminal cancer, elevating Vice-President Earl Warren to the Presidency.
A Liberal Republican, Warren does take something of a different tack than Taft, increasing support to Europe (although too late, much of Europe is embittered by the US's partial withdrawal) and stationing additional forces in the Far East including support of Taiwan & Japan.
Domestically President Warren was engaged by civil rights & education—a major expansion of the American public education system and strong government support to attend College via a made permanent GI Bill that applied to either wartime service or a six year commitment to the US Armed Forces. The new GI Bill also covered most costs of going to University—making it more generous than the old bill.
During this time period the US also moved to a volunteer military but retains the draft for emergencies.
Cilv Rights take a different tack. Without the Warren Court a number of landmark decisions are not taken up, or go different ways. As such Warren's efforts in civil rights are directly seen as federal government interference, pushing the Dixiecrats harder both into considering third party bids and a renewed alliance with hawkish Democrats (Warren, after five years with Taft, has adopted a somewhat isolationist foreign view…*albeit one that does involve more overseas commitments.)
The 1956 election sees Senator Richard Russell come close to taking the nomination as Senator Kefauver siphons many Northern liberal delegates—this forces Adlai Stevenson to once again step in and run as the compromise candidate in a near-repeat of 1952. (W. Averell Harriman decides to stay in New York, where Rockefeller will defeat him in the '58 governor's race.)
However President Warren (and his running mate, California Senator William F. Knowland) is viewed well among the nation, and handily defeats Governor Stevenson. Notably the South returns to the Democrats. Whereas Taft won a number of Southern states in '52, the entire South goes Democratic in '56—partially helped by Stevenson's running mate, Senator John Sparkman.
In his second term President Warren moves sharply to the left on civil rights and post-war domestic tranquility is shattered by increasing violence in the South between blacks and whites. Federal troops help matters in the short term.
Overseas and partially prompted by Vice-President Knowland Warren continues to shift the US out of it's Taft isolationist phase. Among other things US advisors go to Viet Nam, military support to the Nationalists in Taiwan is stepped up, pressure is brought to bear on the Japanese to expand their military, significant armed forces are committed to Europe (which is generally unwelcome, as the current view of America is not good), and meddling in various third world countries grows.
The Republican Knowland/Senator Irving Ives ticket is defeated by Democratic Senator John F. Kennedy (and running mate, Senator Henry M. "Scoop" Jackson) in the election of 1960.
Kennedy works to expand the military and strengthen overseas ties but is bediviled by civil rights (
jump here for my JFK lives/civil rights go bad mini-timeline. It's mostly applicable, with the different background of OTL above generally making things even worse for the USA.)
We're in the '70s now and the USA is in slow motion collapse. The price of oil is skyrocketing, the whites have left the cities to heavily armed black civil right forces and the South is a free-for-all.
Wallace narrowly won the '72 election, and has bombed North Vietnam into the stone age and is making noises about rolling back communism.
It's early in the morning of 6 October 1974 and Israel is caught napping as Arab forces strike hard and fast.
The USSR (waiting for an opportunity) announces that they will stabilize the situation, and Soviet tanks start rolling into Iran. Within a month Arab forces withdraw to try and stop the Red Army but one by one the USSR sweeps through the countries of the Middle East. (They also hand Israel their pre-6 October borders and assure them they have no interest in violating them.)
President Wallace condemns the move but with American troops tied up in Indochina and Europe is unable to do more than move naval assets. However, Wallace quickly decides that hurting the Soviets is important to American self-interest.
Planes from six US carriers begin roaming through the Middle East, destroying everything related to oil production in a scorched earth strategy to deny the Soviets anything of value. The USSR in turn shifts its vast air forces in Europe southward, sinking a pair of US carriers despite massively one-sided loss ratios.
In turn the US levels Vladivostok from planes out of Japan and the undeclared war steps up to involve submarines stalking each other in the dark quiet of the northern Atlantic and across the US's supply lines in the Pacific.
Relations with Europe, badly strained since the cancellation of the Marshall Plan decades ago finally collapse—dependent as they are on foreign oil (excepting France, mostly). Western Europe has a lot fewer sources of oil these days.
American troops begin the long voyage home from Europe, many to be sent straight to Viet Nam.
Domestically ever-increasing oil prices have basically grounded the US economy as suburbs are simply not connected with anything other than roads. A crash infrastructure program centring on rail and nuclear power that's been ongoing for a few years is paying dividends, but only in the denser parts of the country.
Most Northern/Mid-Atlantic/Great Lakes US cities are dark holes in the landscape these days, well equipped black forces in control of the ruins as federal troops barricade them out of existence.
Washington, D.C. is the most heavily garrisoned city in the world but four Senators and eighteen Representatives have so far been killed by black snipers.
New England's quiet towns and rolling hills are kept that way by a combined state-federal DMZ stretching north of NYC to Canada.
In the South the situation has quieted done, by the wholesale slaughter of blacks by state forces. The countryside remains a dangerous place, but the cities are working.
The Midwest and the Far West are the only regions still more or less functioning as normal, keeping America fed and connected to the Far East.
I could go on but the US is pretty screwed so far.