By Ted Hesson and Kristina Cooke WASHINGTON (Reuters) – U.S. President Joe Biden said last month that the United States would accept up to 100,000 Ukrainians fleeing Russia’s invasion, but lawmakers and advocates have urged the Democratic president to speed up refugee and visa processing. While several thousand Ukrainians have entered the United States via the border with Mexico and some on legal visas, only 12 Ukrainians came through the U.S. refugee program in March. WHY HASN’T THE U.S. TAKEN IN MORE UKRAINIAN REFUGEES? More than 4 million people have fled Ukraine to neighboring countries si…