The necessity of guarding the Western and Atlantic Railroad was an ever-present concern with Sherman. Forrest and his cavalry force were in northern Mississippi waiting for him to get far enough on the way to Atlanta for them to pounce upon the iron way and tear it to ruins. To prevent this General Samuel D. Sturgis, with eight thousand troops, was sent from Memphis against Forrest. He met him on the 10th of June near Guntown, Mississippi, but was sadly beaten and driven back to Memphis, one hundred miles away. The affair, nevertheless, delayed Forrest in his operations against the railroad, and meanwhile General Smith's troops returned to Memphis from the Red River expedition, somewhat late according to the schedule but eager to join Sherman in the advance on Atlanta. Smith, however, was directed to take the offensive against Forrest, and with fourteen thousand troops, and in a three days' fight, demoralized him badly at Tupelo, Mississippi, July 14th-17th. Smith returned to Memphis and made another start for Sherman, when he was suddenly turned back and sent to Missouri, where the Confederate General Price was extremely active, to help Rosecrans. To avoid final defeat and to win the ground he had gained had taxed Sherman's powers to the last degree and was made possible only through his superior numbers. Even this degree of success could not be expected to continue if the railroad to the North should be destroyed. But Sherman must do more than he had done; he must capture Atlanta, this Richmond of the far South, with its cannon foundries and its great machine-shops, its military factories, and extensive army supplies. He must divide the Confederacy north and south as Grant's capture of Vicksburg had split it east and west. Sherman must have Atlanta, for political reasons as well as for military purposes. The country was in the midst of a presidential campaign. The opposition to Lincoln's reëlection was strong, and for many weeks it was believed on all sides that his defeat was inevitable. At least, the success of the Union arms in the field was deemed essential to Lincoln's success at the polls. Grant had made little progress in Virginia and his terrible repulse at Cold Harbor, in June, had cast a gloom over every Northern State. Farragut was operating in Mobile Bay; but his success was still in the future.