(In your opinion? )
Well, one hell of a blunder was Mark Clark's order to capture Rome, after the Battle of Monte Cassino, instead of trapping the German 10th Army with the units that managed the breakthrough in Anzio, which was what Alexander (commander of the 15th Army Group) had ordered him. After one of the bloodiest battles the Western allies had fought, total victory was not achieved, Seven german divisions managed to escape through the gap Clark left open, and went forth to strenghten the Gothic Line. Result: The Italian front was the last to close in the war on Europe, while otherwise the allies would have much a clearer path, though still moving slowly due to the geography of the peninsula.
Truscott, the commander of the division that was supposed to close the gap, later wrote:
"...I was dumbfounded. This was no time to drive to the northwest where the enemy was still strong; we should pour our maximum power into the Valmontone Gap to insure the destruction of the retreating German Army. I would not comply with the order without first talking to General Clark in person. ...[However] he was not on the beachhead and could not be reached even by radio. ... such was the order that turned the main effort of the beachhead forces from the Valmontone Gap and prevented destruction of Tenth Army. On the 26th the order was put into effect
There has never been any doubt in my mind that had General Clark held loyally to General Alexander's instructions, had he not changed the direction of my attack to the northwest on May 26, the strategic objectives of Anzio would have been accomplished in full. To be first in Rome was a poor compensation for this lost opportunity"
It makes it even worse that, apparently, Mark Clark's decision was on the basis of not letting the BRITISH liberate Rome first. What kind of line of thought is that?! Here you got, your ally, his army outnumbers yours greatly (The 8th army was much bigger than the 5th if im not mistaken) you two are fighting together hand in hand, and then you just decide to ruin all the strategic operation so you get the fame of liberating rome?!
Well, truth be told -most- american generals in world war 2 were more worried about being on the papers and bashing the british counterparts than anything else... (Patton, Bradley, Clark.....)