US President Donald Trump has tweeted an endorsement for a government shutdown, while also urging Republicans to consider changing Senate rules to make it easier to pass spending and other bills without any Democratic support.
"Our country needs a good 'shutdown' in September to fix mess!" he wrote on Tuesday.
Mr Trump also backed the so-called "nuclear option" for legislation but added that the party could strengthen its hand by winning more Senate seats in the 2018 congressional election.
Democrats - and some Republicans - quickly denounced his call to close the federal government in a spending fight just as both parties were closing in on a final measure to fund agencies through September.
"Here we saw Democrats and Republicans working together in the best traditions of the Senate, and the president disparages it in a way that's destructive," Democratic Senate Leader Chuck Schumer said.
Senator John Cornyn of Texas, the No. 2 Republican in the Senate, told reporters: "I just don't agree."
Mr Trump said his fellow Republicans had to acquiesce to Democratic demands in a government spending bill negotiated this week because the party's majority was too slim.
"The reason for the plan negotiated between the Republicans and Democrats is that we need 60 votes in the Senate which are not there! We either elect more Republican Senators in 2018 or change the rules now to 51%," Mr Trump wrote on Twitter.
Republicans last forced a government closure in 2013 for 17 days. Democrats said Mr Trump would shoulder the blame for any shutdown now.