On the eve of Iowa’s Republican caucuses, Democratic Gov. J.B. Pritzker on Sunday dismissed new national polling showing low job approval for President Joe Biden, saying “the battle hasn’t been joined” until GOP voters pick their nominee. Pritzker, who is scheduled to be in Des Moines on Monday for the caucuses as a surrogate for Biden’s reelection, acknowledged on ABC’s “This Week” program that former President Donald Trump is the likely GOP nominee based on polling. But he criticized the entire Republican field — including Florida Gov. Ron DeSantis and former U.N. Ambassador Nikki Haley — as…