Thousands of Filipinos filled the streets of Manila on Sunday to protest the government, which they accuse of misappropriating billions of dollars that were designated for flood relief projects. Greenpeace, an environmental group, later estimated that about a trillion Philippine pesos, or $17.6 billion, that was supposed to help the country confront chronic and deadly flooding had been embezzled. To address the issue, Mr. Marcos created an independent commission to probe the flood-control projects, and a Senate committee is conducting its own investigation. Both the Senate president and the House speaker have already been replaced as part of the fallout from the scandal, which follows years of infrastructure issues that have worsened as climate change exacerbates flooding. Mr. Marcos has sought to align himself with the protesters.