THE United States is taking charge in earthquake-devastated Haiti as thousands of troops and tonnes of aid begin arriving in the impoverished Caribbean nation. US President Barack Obama, responding to the first large-scale humanitarian disaster of his presidency, has pledged $US100 million to Haiti with more to come. "I will not put up with any excuses for us not doing the very best in this time of tragedy,'' Mr Obama said. He announced that the "first waves" of the US response were in place including two search-and-rescue teams on the ground, Coast Guard cutters in the port, the US Southern...