House Republicans added an amendment that would fund the government until December, a month longer than the Senate version. They also added a "conscience clause" to the one-year delay amendment to allow employers and insurance plans to refuse to cover birth control.
In a sign that the House Republicans don't expect the Senate to accept their changes, House leaders held a separate vote to ensure that the military gets paid in the event of a government shutdown.
Officials estimate the military pay could be affected by a shutdown as soon as October 14, and the GOP move was considered a political gesture to shield the party from criticism that its brinksmanship could hurt U.S. fighting forces.
Obama not backing down
Tea party conservatives want to halt Obamacare now, just as full implementation of its individual health care exchanges begins in the new fiscal year starting Tuesday.
More moderate Republicans, such as veteran Sens. John McCain of Arizona and John Cornyn of Texas, criticize the strategy of tying a government shutdown to undermining the health care reform law passed by Democrats in 2010 and upheld by the Supreme Court last year.
Obama said Friday that new exchanges for private health insurance under the reforms will open this week as scheduled -- even if there is a government shutdown.
"The House Republicans are so concerned with appeasing the tea party that they have threatened a government shutdown or worse unless I gut or repeal the Affordable Care Act," Obama said. "That's not going to happen."
Even if the government were to shut down, Obamacare would probably continue anyway. That's because most of the funding for Obamacare comes from new taxes and fees as well as from cost cuts to other programs like Medicare and other types of funding that would continue during a government shutdown.
Congress' research arm, the Congressional Research Service, prepared a memo for Sen. Tom Coburn, R-Oklahoma, that suggested an effort to use the government shutdown as leverage to force Democrats to delay implementing the law would not really work because the law will continue regardless of a shutdown.
Plus, the law would still be in effect, so its many new requirements -- everything from forcing insurance companies to cover anyone who wants insurance, to requiring Americans to carry health insurance or pay a fine -- would still be in effect, too.
Republican leaders in both chambers don't want a shutdown now over the spending issue, for political and negotiating reasons.
They fear the optics of Republicans being blamed for a shutdown, and also want to exert as much leverage as possible for the GOP's agenda at the upcoming deadline to raise the federal debt limit.
The debt ceiling
The shutdown showdown comes a few weeks before another fiscal deadline -- the need to raise the nation's debt ceiling so the government can pay all its bills.
Treasury Secretary Jack Lew said last week the limit on how much the government can borrow must be increased by October 17 or the nation could be technically in default.
Analysts warn of severe economic impact from any doubt cast over whether the U.S. would meet its debt obligations. A similar bout of congressional brinksmanship over the debt ceiling in 2011 led to the first-ever downgrade of the U.S. credit rating.
Boehner faces the same rift in his caucus over the debt ceiling issue, with tea party conservatives pushing to undermine Obamacare and fulfill other Republican priorities in return for what Obama calls the responsibility of Congress to make sure America can pay its bills.
On Thursday, Boehner had to delay introducing a GOP debt ceiling plan after conservatives complained the proposed package failed to include enough budget cuts and significant changes to entitlement programs.
The initial proposal by House GOP leaders, which would raise the debt ceiling for a year, included a one-year delay of Obamacare, provisions to roll back regulations on businesses, tax reforms and approval of the Keystone XL oil pipeline.