I'll just point out that August 6 is the Feast of the Transfiguration, and so not really a proper day for fasting (though at least some bishops are cool with it).
Also, if I'd been asked, I think instead of referring to Joel 2 -- I assume they mean vv 12-17, give or take:
Yet even now, says the LORD, return to me with your whole heart, with fasting, and weeping, and mourning; Rend your hearts, not your garments, and return to the LORD, your God. For gracious and merciful is he, slow to anger, rich in kindness, and relenting in punishment. Perhaps he will again relent and leave behind him a blessing, Offerings and libations for the LORD, your God. Blow the trumpet in Zion! proclaim a fast, call an assembly; Gather the people, notify the congregation; Assemble the elders, gather the children and the infants at the breast; Let the bridegroom quit his room, and the bride her chamber. Between the porch and the altar let the priests, the ministers of the LORD, weep, And say, "Spare, O LORD, your people, and make not your heritage a reproach, with the nations ruling over them! Why should they say among the peoples, 'Where is their God?'"
I might've proposed Jonah 3:4-5:
Jonah began his journey through the city, and had gone but a single day's walk announcing, "Forty days more and Nineveh shall be destroyed," when the people of Nineveh believed God; they proclaimed a fast and all of them, great and small, put on sackcloth.
Better, perhaps, to see your country as Nineveh than as Zion.
(Also, I'm not altogether sure those Texans aren't eyeing Joel 2:20.)