WASHINGTON (AP) — A Republican senator in a tough re-election race is attacking his top Democratic rival for supporting more Syrian refugees in the U.S., marking the issue's first appearance in Senate campaign advertising. [...] his focus on the issue highlights the Republican view that it can be a vulnerability for Democrats, especially those like Duckworth who opposed recent GOP legislation cracking down on the refugee program. Duckworth, a military veteran, has been outspoken about the need to show compassion to refugees, many of whom are women and young children themselves victimized by the Islamic State.