By Richard Cowan and David Morgan WASHINGTON (Reuters) – If Republicans win control of the U.S. House of Representatives in November’s midterm elections, they expect to use a powerful and potentially dangerous tool as leverage in their dealings with Democratic President Joe Biden: The federal debt ceiling. The U.S. Treasury is expected to reach its mandated $31.4 trillion borrowing limit in 2023, and Republicans ranging from hard-line conservatives to moderates see that as an opportunity to curb Biden’s spending on Democratic initiatives such as climate change and new social programs. “It’s cr…