Grant decided to bring his whole army to bear against the city, abandoning a previous plan to turn west and cross the Big Black River at Edwards and Bolton. The previously planned movement was viewed as too risky with Johnston and the Jackson garrison left in the Union army's rear, especially as McClernand's men had also encountered part of Pemberton's force elsewhere simultaneously as the battle at Raymond. McClernand was ordered to move to Raymond, McPherson was to head northeast to Clinton and then strike Jackson, and Sherman was to approach the place from the southwest. A successful action against Jackson had the potential to remove its value as a Confederate reinforcements center and clear the area of Confederate troops. From Pemberton's perspective, a Union movement against Jackson had the ability to sever the key railroad supply lines to Vicksburg. As a result, the Confederates would need to defeat Grant in open battle outside of the defenses of Vicksburg, and Pemberton's army moved east for this purpose. Johnston had issued an order for Pemberton's force to join with his at Clinton, but this was not possible due to Union control of the area. On May 14, the Union army attacked Jackson. Johnston withdrew his men from the city, Gregg performing rear guard duty. Grant's army then turned west and encountered Pemberton's men, who were attempting to make a stand east of Vicksburg. On May 16, Pemberton's men were defeated at the Battle of Champion Hill, and after a defeat in a rearguard action at the Battle of Big Black River Bridge the next day they withdrew into the Vicksburg defenses. Union attempts to take the city by direct assault on May 19 and 22 failed, and Grant placed Vicksburg under siege. Supplies within the city eventually ran low, and with no hope of escape Pemberton surrendered the city and his army to Grant on July 4, ending the siege of Vicksburg. The capture of Vicksburg was a critical point in the war. Assessment Bearss describes McPherson's handling of the battle as "not a success" and as "far too cautious or, perhaps worse, timid", citing his piecemeal deployment of his troops and ineffective use of his artillery advantage. Miller also states that McPherson mismanaged the battle and called the decision not to pursue a mistake. Ballard concludes that McPherson had not formed an overall plan of command, instead just feeding troops