WASHINGTON (AP) — Former Massachusetts Gov. Mitt Romney is adding to his big lead in the race for convention delegates by winning the Indiana Republican presidential primary, inching closer to the number needed to clinch the GOP nomination.Romney won at least 18 delegates in Indiana on Tuesday, with nine still undecided. He is poised to win even more delegates in primaries in North Carolina and West Virginia. In all, 107 delegates are at stake in the three contests.Romney has a commanding lead in the race for delegates with 874. He is 270 delegates shy of the 1,144 he needs to clinch the nomination — a gap he could close by the end of the month.The only other Republican left in the race, Texas Rep. Ron Paul, has 94 delegates.