For an argument by William Freehling that James Buchanan's greatest blunder during the "secession winter" was not being too passive but on the contrary (for a few crucial days) too activist, see
https://opinionator.blogs.nytimes.com/2011/01/05/james-buchanans-activist-blunder/
POD: Buchanan unequivocally orders Anderson, "We've got an informal truce, stay put at Moultrie unless actually fired on, no matter how much danger you think you're in." Anderson and his men remain at Moultrie instead of escaping to Sumter, and there is no "Star of the West" incident.
What then? Freehling argues:
"All this military furor occurred before any state except South Carolina had seceded and during the very days when Lower South voters and convention delegates were deciding on disunion. Thanks to Buchanan’s activism, at this precarious juncture the issue swerved from the expediency of secession to the right to deter federal 'coercers' and to the patriotism of the brave boys who stood up to the 'invasion.' Amidst that uproar, many previously uncertain Lower South voters enthusiastically embraced disunion, helping to propel six southern states toward South Carolina...
"But the question remains: Wouldn't the six other Lower South states have joined South Carolina in January in any case, even if Buchanan had prolonged his December stall on military intervention? Probably. In Florida and Mississippi, the military excitements could have only fattened the secessionists already huge majorities. But elsewhere, the aftermath of Buchanan's Star of the West decision just may have deflected the verdict. Especially in closely contested Georgia and Louisiana, public uproars may have boosted the secessionists to their razor-thin victories.
"The history that did not happen must remain uncertain. But the history that did happen clarifies why secessionism survived its early southern doubters..."
My basic problem with this analysis is that in the Lower South, while the victory of the Immediate Secessionists was indeed narrow in some of the states and might conceivably have been avoided with different policies in Washington, Immediate Secessionists *combined* with those who favored staying in the Union for awhile only if Lincoln met certain conditions he was unlikely to meet would certainly be a majority. These conditions would include agreement to the Crittenden proposals (protection of slavery in any territories south of the Missouri Compromise line including those "hereafter acquired") and refraining from using "coercion" against those states which did choose to secede--with attempts to collect revenues offshore being included under "coercion." In short, at least once South Carolina had seceded, the real choice in the rest of the Lower South was probably between Secession Now and Secession Later.