"Anyone who thought that Fillmore lacked spine was now disabused"

I have explained in a number of previously published posts how Millard Fillmore's firm and decisive actions in early August 1850 formed the basis for resolution of the crisis that had been building for four years, ever since David Wilmot had introduced his fateful Proviso in August 1846.  In a nutshell (see the posts linked above for more detail), the newly-installed president made clear to the State of Texas that the federal government would fight if state forces attacked the New Mexico territory.

In his newly-published book America's Great Debate: Henry Clay, Stephen A. Douglas, and the Compromise That Preserved the Union, Fergus M. Bordewich points out the guts that this move took:

The following day, August 6 [1850], Fillmore sent his own message to Congress.  [Secretary of State Daniel] Webster may have contributed to it, but to give the president his due, anyone who thought that Fillmore lacked spine was now disabused.  A weak man might well have capitulated to the Texans: Fillmore dug in his well-polished boots.  The president declared unequivocally that New Mexico was federal territory, and that Texas enjoyed no rights or powers beyond her state limits.  "If Texas militia march into any of other States or into any Territory of the United States, there to execute or enforce any law of Texas, they become at that moment trespassers; they are no longer under the protection of any lawful authority, and are to be regarded merely as intruders," he declared.  Should the laws of the United States be opposed or obstructed in any way, it was his duty as commander-in-chief to employ the armed forces as they were needed.

The response to Fillmore's message, especially from northerners in Congress, was highly favorable; from Newport [Rhode Island], Henry Clay sent a telegram offering the president his full support.  The sleekly groomed Fillmore might not be the soldier that hard-edged [Zachary] Taylor had been, but his meaning was equally unmistakable: the United States was ready to go to war.

The president's message shifted the focus from the California issue to Texas-New Mexico.  And the combination of the president's "stick" and the "carrot" represented by the Texas bond bill did the trick:

The real question was: what would [the two Texas senators, Thomas Jefferson Rusk and Sam Houston] do?  Without their support, no compromise would work. . . .  Both . . . knew that federal troops were en route to New Mexico, that the president was firmly committed to resist an invasion, and that without the camouflage of the Omnibus Texas stood no chance of winning congressional recognition for its entire elephantine claim.  Some Texans were also having second thoughts.  "It is unpleasant to impoverish the state and tax our people with insupportable burthens to make war against the U.S. although it is as we all know on our soil," one uneasy constituent wrote to Rusk.

It was over within a matter of days.  On August 9 Rusk and Houston announced their support for the Texas-New Mexico measures.  That day, Stephen Douglas' motion for a third reading of the bill squeaked by, 27 to 24.  "[T]he Texans had tipped the balance."  The final vote on the bill, later that evening, "was decisive, if anticlimactic": 30 votes to 20.

About the illustration at the top, entitled Capability and Availability:

Sharply critical of both the Democratic and Whig choice of presidential candidates in 1852, the artist laments the nomination of two soldiers, Winfield Scott (center) and Franklin Pierce (far right), in preference to several more "capable" statesmen who appear at left. The latter are (left to right): Samuel Houston, John J. Crittenden, Thomas Hart Benton, Millard Fillmore, John Bell, Lewis Cass, Stephen A. Douglas, and Daniel Webster. Most prominent in the group are Fillmore, Cass, and Webster, who also sought the presidential nomination in 1852. Fillmore: "I have sought more anxiously to do what was right; than what would please, and feel no disappointment, at finding that my Conduct has, rendered me an unavailable candidate." Cass: "We have been partizans where we differed in opinions as to the best means of promoting the prosperity and happiness of our native land, but we cast aside, party when we stood Shoulder, to Shoulder, for the Constitution & the Union." Webster: "It is not our fortune to be, or to have been successful Millitary Chieftains. We are nothing but painstaking, hardworking, drudging Civilians, giving our life, and health, and strength, to the maintenance of the Constitution and upholding the liberties of our country." Columbia, draped in stars and stripes and grasping the hands of Scott and Pierce, responds: "I acknowledge your noble services, worth and Constant devotion most Illustrious sons, and that you have the long experience, Sound sense and practical wisdom which fit you to receive the highest honor in my power to bestow, but you are "not Available." " "Availability," in the contemporary lexicon, meant the quality of broad popular appeal. Scott and Pierce were both distinguished in the Mexican War. Scott, holding a liberty staff and Phrygian cap, proclaims: "You see Gentlemen it is "availability" that is required and that is "my" qualification." Pierce holds a shield adorned with stars and stripes, adding, "I am a "Great" man and have done the country "Great" Service! I never knew it before; but it "must be so;" for the Convention has declared it, and the Democracy affirm it." Before his nomination by the Democratic convention of 1852, Pierce was a relatively little known New Hampshire attorney--a fact which Whig publicists tended to exaggerate. Pierce had, after all, served as a two-term congressman and senator from New Hampshire.