By Trevor Hunnicutt, Patricia Zengerle and Richard Cowan WASHINGTON (Reuters) -President Joe Biden warned Republicans on Tuesday that they would give Russia a “Christmas gift” if they failed to provide additional military aid to Ukrainian President Volodymyr Zelenskiy, whose meeting with a top U.S. lawmaker concluded without a commitment for more support. Zelenskiy traveled to Washington to plead for money to back Ukraine in its war with Russia, but he faced a skeptical reception from key Republican lawmakers. Mike Johnson, the speaker of the House of Representatives, would not agree to suppor…