By David Morgan WASHINGTON (Reuters) – Republican U.S. Senator Lindsey Graham proposed new national restrictions on abortion on Tuesday, two months before the Nov. 8 midterm elections in which the abortion issue has emerged as potential albatross for Republican candidates. With control of the Senate up for grabs, and some jittery Republican candidates softening their positions on abortion, Graham announced legislation that would ban the procedure after 15 weeks of pregnancy nationwide. The move carries political risks. Polls have shown the issue of abortion has increased in importance for Demo…