WASHINGTON (AP) — Facing weakening support among Hispanics, President Barack Obama is expressing deep frustration over what he called an inaccurate and damaging perception that he can fix the nation's flawed immigration system on his own.Obama said Wednesday during a White House roundtable targeting Hispanic voters that the idea of him unilaterally changing laws "is just not true."Obama said comprehensive immigration reform continues to be a "top priority" for his administration. But he blamed Republicans in Congress for failing to join Democrats in supporting legislation that would address the flow of foreigners into the U.S. and deal with illegal immigrants already in the U.S.A strong majority of Hispanics supported Obama's election in 2008. But his support among Hispanics has declined, as it has in the broader population.