President Barack Obama hopes to rally new momentum behind the push for an immigration overhaul by explaining why he thinks a comprehensive approach is the only way to fix what he and others say is a system badly in need of repair. Obama was laying out his rationale in a speech Thursday, his first as president on the issue. Obama wasn't expected to announce any new proposals or policy changes. But feeling pressure from a range of supporters, he was aiming to jump-start the effort he had promised to make a priority in his first year and which advocates had...