The White House is making a big push to rally members of Congress and the US public behind President Barack Obama's plan for a military strike against Syria.
His administration says the government of Syrian president Bassar Assad used chemical weapons in an attack last month near Damascus and that a strong US response is needed to deter the future use of deadly chemicals.
Syria claims rebels carried out the August 21 attack.
Mr Obama's chief of staff Denis McDonough is set to make the White House's case during interviews on five Sunday talk shows.
Vice President Joe Biden plans to host a dinner on Sunday night for a group of Senate Republicans. Lawmakers should also expect more phone calls from top officials.
Mr Obama is to give a national address on Tuesday night.