Does "they get bitter" mean "they become tougher"?

Context:

Last week on the Visual Thesaurus, William Safire and Nancy Friedman
both weighed in on "Bittergate," the political furor that arose over
Senator Barack Obama's comments about small-town Pennsylvanian
voters ("It's not surprising, then, they get bitter, they cling to guns or
religion"). Now Obama has found himself under the microscope again
for his use of a particular word, but this time the context is more
"sweet" than "bitter." Responding to a question from television reporter
Peggy Agar at an automobile plant outside of Detroit, Obama said,
"Hold on one second, sweetie." Later he left Agar a voicemail
apologizing about using the word sweetie to address her, calling it a
"bad habit of mine." Lisa Anderson of the Chicago Tribune wryly wrote,
"Welcome to 'Sweetie-gate,' a place paved with eggshells, where terms
of endearment turn into political peccadilloes at the drop of a
diminutive."