Perhaps the BEST B1G Forum anywhere, here at College Football Fan Site, CFB51!!!

So many what-ifs. I'm left grateful to the people who planned it, the men who executed it, and for the aftermath that led to a safer, better world. 

Can the Allies hold a single beach head (Utah)? It would take a great deal of naval and aerial support--both of which the Allies had. And it would take a huge effort to pour men, weapons, and supplies in there under intense fire and counter attacks. Would have been ugly, either way.

Certainly the Germans would have been able to better concentrate on the Russians if they were able to turn the invasion back. Enough to stem the tide of the war and sue for peace with the Russians? Perhaps. If so, how do the U.S. and U.K. respond to a Nazi western Europe and a Communist eastern Europe? 

If not, a Russian dominated Europe would have looked much, much different. Would Russian occupation of western Europe lead to the U.S. and U.K. going to war with Russia at a time when only the U.S. had nuclear capability? Certainly possible.

And that nuclear capability thing--coming essentially in August '45--puts an interesting spin on any potential direction for an ongoing war in Europe.

Lots of bad possibilities.

Even domestically, some big differences.  Does a defeat there cause FDR's health to fail more quickly.  MacArthur was already a popular choice for the GOP nomination, and maybe calls for a change in a commander in chief bolsters him to a nomination, and ultimate victory.

Even if 1944 goes the same, there's no way Truman wins in 1948.  Is it Dewey?  Does the Dixiecrat/Progressive split actually divide the party into a true three party system, rather than splintering off, without Truman sort of holding the middle ground?

Eisenhower is certainly out of his command, and obviously not a presidential candidate in 1952.  

Another interesting twist is that we may have wound up with the Kennedys, simply sooner.  Joseph Sr.'s anti-war, anti-Britain, anti-semetic leanings may have made him a popular choice as a Democrat alternative (not sure anyone but Ike would have swung the country red anytime soon), and he almost certainly would have negotiated with Hitler

Would Russian occupation of western Europe lead to the U.S. and U.K. going to war with Russia at a time when only the U.S. had nuclear capability? Certainly possible.

I don't think a failure on June 6, 1945 would have led to complete Soviet domination in Europe for several reasons. 

First, the US/UK invasion of Italy was still proceeding and the later US/UK invasion of southern France could still have been conducted.  Additionally, even if the invasion on June 6 had failed, it still would have been reasonably possible to simply keep stockpiling material in Britain and try again later. 

Second, and more important, the US conducted the Trinity Test just a 13 months and 10 days after D-Day.  On July 16, 1945 the world entered the nuclear age about 35 miles from Socorro, New Mexico. 

As it happened, the Russians got to Berlin in early May, 1945 but Europe's preeminent anti-communist had wasted huge amounts of German war-making capability on a futile effort to turn back the US/UK forces the previous December (See Battle of the Bulge).  Without a US/UK army conquering France and threatening Western Germany as well as capturing much of Germany's industrial heartland in the Ruhr it is obvious that the Germans would have been better able to delay the Soviet advance.  I'm not saying that they could have stopped the Russians, just that they could have slowed them down more than they already did. 

What this means is that even if D-Day had been a colossal failure, there still would have been viable German targets for US atomic weapons when those became available in August, 1945.  The net result would have been a MASSIVE increase in German civilian casualties as US Atomic weapons obliterated German Cities.  B29's operating out of southern England could have reached any city in Germany. 

There is also another scary possibility.  In preparing to invade Japan, one possibility that was considered was to use a/an Atomic Bomb(s) to clear the beaches immediately before landing.  The long-term consequences for the US/UK troops landing on recently nuked Japanese beaches would have been catastrophic but that wasn't well understood then and the Army had a war to win.  If D-Day had failed it is not unlikely that A-Bombs would have been used to clear the way for a second try in August, 1945 with the Russians probably still in Poland. 

I don't think that Soviet domination of Europe would have been total largely because from July 16, 1945 until August 29, 1949 the US had an absolute monopoly on nuclear weapons.  Even after that, the US had much better delivery systems than the Soviets for another decade or so. 

Was there a German city of any consequence left standing by August 1945?

One reason for targeting Hiroshima and Nagasaki was they had been largely left unbombed, Kyoto in an attempt to preserve history as I recall.

Was there a German city of any consequence left standing by August 1945?

One reason for targeting Hiroshima and Nagasaki was they had been largely left unbombed, Kyoto in an attempt to preserve history as I recall.

From Wiki, here is a map of what the Germans still held as of the Dresden Bombing in February, 1945:
https://en.wikipedia.org/wiki/Bombing_of_Dresden_in_World_War_II#/media/File:1945-02-15GerWW2BattlefrontAtlas_reworked.jpg

I thought that the Belligerents list from the wiki article really sums up the German situation at the time.  The RAF sent 769 heavy bombers while the USAAF sent another 527 heavy bombers and 784 P-51's as escorts.  Against this massive aerial armada of more than 2,000 aircraft the Germans put up 28 fighters. 

Southern German cities had only recently come into US/UK range so yes, I think there definitely would have been plenty of targets available in an alternate history in which the Germans pushed Ike back into the Channel on June 6, 1945. 

This is well said and I agree with the whole post, not just the part I quoted.  As a practical matter, @CWSooner is absolutely right.  The allies had near-total air-supremacy, near-total naval-supremacy, and LOTS more men and equipment than the Germans could put up in resistance. 

Yes, I took the question as what if the entire plan failed.

Hell, Ike at least thought it enough a possibility that he had a letter in his pocket for release in that event.