President Obama on Monday said a government shutdown would deliver a blow to the economy and accused Republicans of re-fighting lost political battles as lawmakers remained deadlocked on a spending bill ahead of a midnight deadline.

The Senate earlier Monday rejected a House spending bill that would delay Obamacare for one year, while GOP leaders insisted they would not support a so-called “clean” resolution to keep the government funded.

Barring a surprise solution, the first government shutdown in 17 years appears imminent.

“It does not have to happen,” Obama said in a hastily arranged press conference from the White House briefing room. “All of this is entirely preventable if the House chooses to do what the Senate has already done.”

Given the lack of progress on Capitol Hill, however, the president did not appear optimistic less than seven hours before a government shutdown.

“House Republicans continue to tie funding of the government to ideological demands,” he complained.

The president framed a government shutdown in economic terms, arguing it would keep Americans out of work and inflict another self-imposed wound on a slowly rebounding jobs market.

“Office buildings would close, paychecks will be delayed, vital services ... would be hamstrung,” he lamented. “Business owners would see delays in raising capital … veterans who sacrificed for their country would find their support centers unstaffed.”

Both sides have hunkered down, with Republicans and Democrats accusing the other camp of sticking to rigid, uncompromising positions.

The White House says Republicans are making demands rejected by voters when Obama was reelected. Republicans counter that the only way to get Obama to commit to spending cuts, is through negotiations tied to these high-stakes fiscal clashes.

Obama once again refused to negotiate around his signature legislative achievement: Obamacare. He vowed that the health exchanges would go ahead Tuesday as planned.

For weeks, both Republicans and Democrats have assumed the other side would blink.

It now appears likely that federal workers will face involuntary furloughs and Washington museums and landmarks will shutter on Tuesday. And ahead of the looming shutdown, the stock market dropped, with the Dow, NASDAQ and S&P all registering losses.