A stopgap funding bill was passed by the US House of Representatives and Senate, and signed into law by President Donald Trump in order to end the second government shutdown this year.
Despite holding a majority in the House, the Republicans were unable to pass the bill due to 67 dissenting Republicans, including Rand Paul, who ran out the deadline to pass the bill.
Mr Paul objected to a deficit in the bill caused by a nearly $US300 billion increase in military and domestic spending over the next two years.
Mr Paul objects to the shift away from fiscal conservatism in Republican thinking, which is changing rapidly under the Trump administration.
“I ran for office because I was very critical of President Obama’s trillion-dollar deficits,” Mr Paul told fellow senators.
“Now we have Republicans hand in hand with Democrats offering us trillion-dollar deficits. I can’t … in good faith, just look the other way because my party is now complicit in the deficits. Really who is to blame? Both parties.”
Mr Trump is expected to release a fiscal 2019 budget plan on Monday, but this is already drawing criticism for unrealistic projections.
The new budget reportedly relies on assumptions such as an economic growth rate of 3.2 percent next year, much higher than the 2.5 percent achieved this year, and above the forecasts for next year.
Optimistic assumptions will make the deficit look better in the budget, but could lead to budget blowouts as reality fails to meet the predictions.