Complex sentence: Traditionally, legislation proposed by the administration would go before the House of Representatives, but an early blunder by Roosevelt--who failed to consult Congressional leaders before announcing the bill--stopped cold any chance of passing the bill in the House.
Split into simpler sentences: Traditionally, legislation proposed by the administration first goes before the House of Representatives. However, Roosevelt failed to consult Congressional leaders before announcing the bill, which stopped cold any chance of passing the bill in the House.