South Korean police were on high alert in Seoul on Tuesday to monitor protests by both critics and supporters of President Donald Trump as the U.S. leader arrived in the country amid concerns over North Korea’s nuclear threats. Surrounded by thousands of police officers and a tight perimeter created by buses, hundreds of anti-Trump protesters rallied at a boulevard near the U.S. Embassy, holding banners that read “No Trump” and “No War.” The demonstrators accused the outspoken president of raising tensions with North Korea and pressuring Seoul to buy more…