> I'm thinking back to Grant's Memoirs, and he said something to the effect that...Van Dorn appeared
> at my secondary supply base at Holly Springs, Mississippi, capturing it. This showed the impracticality
> of moving a long line of supplies through an enemies territory, therefore I determined to abandon my
> campaign into the interior.

That is how Grant remembered it. However, contemporary records show that Grant's campaign into the interior had been terminated for all practical purposes by Lincoln and Halleck.

Put it this way. Let's say Van Dorn's raid had not occured. Sherman would still have been repulsed. Grant still had standing orders to make the riverine campaign the great object of his department. McClernand would have arrived to take command of the "Army of the Mississippi." Grant's two closest advisers, Sherman and McPherson, along with the head of the Navy in the department, had been imploring Grant to take command of the riverine operation in person, and Halleck had given Grant carte blanche to command all of the troops in his department. On top of all this, Grant would have gotten word that McClernand had diverted the operation away from Vicksburg and into Arkansas (Arkansas Post).

There is no chance in hell Grant would have remained in Oxford ... Van Dorn simply expedited Grant's eventual decision.