washington four u.s. senate republicans oil refine state urge trump administration thursday block oil shipments venezuela part u.s. sanction country say could raise cost u.s. fuel consumers unite state sanction president nicolas maduro venezuelan officials maduro establish constituent assembly run socialist party loyalists crack widespread opposition place sanction opec member oil industry senators john cornyn texas bill cassidy louisiana thad cochran roger wicker mississippi say letter see reuters unilaterally block oil export could harm u.s. economy venezuelan people unite state import 740,000 barrel per day oil venezuela white house respond request comment letter address president donald trump believe critical consider role u.s. energy industry refine sector play economic national security interest senators write blockade import could inflict great harm industry burden u.s. taxpayers cost senators say sanction shipments venezuelan oil unite state could also increase likelihood disorderly default venezuela give oil business main source revenue creditors could seize venezuelan oil assets cut government remain source finance also note sanction could expand interest china russia venezuela oil business countries invest venezuela years source say unite state could use heavy crude strategic petroleum reserve hold cavern along gulf coast relieve short-term supply pressure venezuela shipments block nearly 680 million barrel oil reserve drill boom unite state allow government store oil need meet international spare supply agreements senators urge trump avoid blockade venezuela oil shipments