How do you get that sense? Halleck was pushing Grant on to Clarksville etc., like he planned before sending Grant against Ft Henry and Ft Donelson.
I hate to say this, but on 17th February Ft Donelson had fallen, but Grant had not yet followed through and occupied Clarksville. Halleck was concerned that the Army of Central Kentucky (the force that had retreated from Bowling Green) was going to go to move to Clarksville and attack Grant. He wanted more reinforcements.
The remainder of Crittenden's division were already at Paducah, and Nelson's division was sent. On the 23rd, with Grant still being inert, Halleck sent Nelson's division to Clarksville, and ordered Grant to send CF Smith's division with him. This force, under Smith as senior general, occupied Clarksville. They then, under McClellan's orders, went to Nashville along with Crittenden's division to cooperate with Buell's 2 divisions advancing overland from Bowling Green.
Halleck then gave Grant a warning order for a movement against the bridges at Corinth etc., and Grant protested weakness. In fact, it's here that Grant almost gets relieved, as he is being inefficient and is preventing the rapid movements that McClellan is pushing Halleck for.
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At this time, Polk's Corps (Army of Mississippi) is still at Columbus (although about to retreat), and Beauregard's Corps (the Army of Central Kentucky) had fallen back towards Chattanooga. The New Orleans garrison (Ruggles' division at Shiloh) is still in New Orleans, and Bragg's other forces are still at Mobile and Pensacola. The Tennessee river is completely open to Corinth, Florence and Decateur, and Grant's inefficency prevented this being exploited. Hence we end up with Shiloh and Corinth...