White House budget director Mick Mulvaney has warned that a government shutdown in September may be "inevitable" if Democrats don’t “behave better.”

Speaking during the daily White House press briefing, Mr Mulvaney sought to clarify an earlier tweet series from President Donald Trump in which he said that the US needs a “good ‘shutdown’ to fix mess!” after Congress reached a budget deal that will keep the government open until September but didn’t include funding for some of the president’s top spending priorities.

Mr Trump also suggested in the tweets that removing the the Senate filibuster might be a good strategy to pushing through his policies.

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“I think the president is frustrated with the fact that he negotiated in good faith with the Democrats and they went out to try to spike the football and make him look bad,” Mr Mulvaney said. “We've got a lot to do between now and September. I don't anticipate a shutdown in September, but if the Democrats aren't going to behave any better than they have in the last couple of days, it may be inevitable.”

The agreed to budget included several Democratic spending priorities, leading Democrats to cheer the agreement as a victory for them.

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Democrats successfully blocked Mr Trump’s request for funds to begin building a border wall, and were able to push Republicans to withdraw more than 160 riders from the budget that would have stripped funding for environmental defence programs and would have cut back on Wall Street financial regulations.

The agreement would ensure that Planned Parenthood would continue to receive funding, as would energy and science policies. Republicans were, however, able to able to expand defence spending through the budget agreement

Emboldened Democrats like Senate Minority Leader Chuck Schemer said that Mr Trump’s call for for eliminating the Senate filibuster for budget negotiations — a strategy known as the nuclear option that used successfully by Republicans to push through the nomination of Supreme Court Justice Neil Grouch — wasn’t going to happen. Any of Mr Trump’s efforts to push through funding for his many controversial top priorities like a border wall are likely to be stopped in the Senate without Democratic support since the filibuster requires a 60 vote majority to move legislation forward for a vote.