Not to mention the war in 2003 and everything afterwards, as presented by Bush (even if he hasn't personally developed the plan), it was "to bring democracy" there.
Since the US was effectively for years in charge there, since 2003, theoretically, there was certainly enough time and money to finish the second dam.
The US was trying to provide "aid" in protecting the dam in 2007 - I have no idea if it was taken on as a legitimate project or just wallpaper to say "see how we're helping".
I don't have time for fun conspiracy theories, but I'm sure lines can be traced all around construction of the dam, through the bush family, back to infrastructure, etc.
The estimated cost of finishing the second dam is much bigger than the "aid" from the link (the aid was meager $27m, split to 21 contractor), but still orders of magnitude lower that the money spent by the US only on the military in Iraq.
Therefore not surprising, from the 2007 article behind your link:
"In a report published on Tuesday, the Special Inspector General for Iraq Reconstruction (SIGIR) said US-funded "short-term solutions" had yet to significantly solve the dam's problems."
Since the US was effectively for years in charge there, since 2003, theoretically, there was certainly enough time and money to finish the second dam.