By David Lawder and Jason Lange WASHINGTON (Reuters) – The United States is poised to unleash a wider array of sanctions against Russia if Moscow escalates the conflict in Ukraine, denying key Russian financial institutions and companies access to U.S. dollar transactions and global markets for trade, energy exports and financing. But the United States and its allies have never before attempted to cut a $1.5 trillion economy out of global commerce, and it is unclear how much pressure even unified Western sanctions can put on Moscow. A review of World Bank and United Nations trade data shows th…