WASHINGTON (AP) — The government shutdown could last for many days or even weeks because politically safe lawmakers in both parties feel little pressure to compromise.

Heavily gerrymandered districts make many House Democrats and Republicans virtual shoo-ins for re-election, insulating them from everything but the views in their slice of the country. That means some lawmakers can be greeted as heroes back home even if nationally the budget standoff comes to be viewed with scorn.

For decades, lawmakers have redrawn congressional boundaries to pack districts with like-minded people and ensure easy re-election for incumbents. But election results and lawmakers' voting patterns show that the House is more sharply divided along party lines than perhaps at any other point in modern times.

"After every census and reapportionment, the blue districts get bluer and the red districts get redder," said former Rep. Steve LaTourette, R-Ohio, using the colorful terms for liberal and conservative districts. "It's against their electoral interests," he said, for lawmakers from such districts to move toward the center rather than feed "red meat" to their most ideological constituents.

Many House Republicans insist that President Barack Obama curtail all or part of his landmark health care law, which they call "Obamacare." But Democrats, who control the Senate, say it's preposterous to yield ground on a major accomplishment that survived a Supreme Court challenge and Obama's 2012 re-election.

Both sides appear unwilling to budge, thanks to lawmakers' ideological beliefs and the strong support they generally receive from voters back home.

"It might be that both sides are backed into a corner so far that it's hard to get out of," said Rep. Mike Simpson. R-Idaho. "Obama is not going to give up on Obamacare, for either a delay or defunding it," he said. "And I don't see how we can give up on trying."

Constituents calling and emailing his office, Simpson said, generally oppose both the shutdown and the Obama health law. He said the government shutdown could last at least two weeks, which would overlap with the more consequential question of whether to raise the U.S. debt limit to avoid defaulting on obligations.

Like many Republicans, Simpson said the GOP will have more political leverage on the debt ceiling because the stakes will be so high. The White House calls that an irresponsible and unacceptable strategy, and it vows not to negotiate on something that could rock financial markets worldwide and trigger a new recession.

Senate Majority Leader Harry Reid, D-Nev., fully endorsed that view Thursday. He said no conditions can be attached to a "clean" extension of government funding and a hike in the nation's borrowing capacity. If that forces House Speaker John Boehner, R-Ohio, to rely on Democratic votes and possibly lose his speakership to angry conservatives, Reid told reporters, then so be it.

Interviews with House Republicans and Democrats expose the ideological chasm that separates them, and the self-assurance of politicians strongly favored to win next year's election, regardless of the shutdown outcome. One side's reasonableness is the other side's absurdity.

"Something that is very reasonable is for us to give them a one-year CR in exchange for a one-year delay" in the entire health law's implementation, said Rep. Raul Labrador, R-Idaho. A "CR" is a continuing resolution, which would extend government funding at current levels.

Labrador won his last election with 63 percent of the vote, and Obama lost Idaho to Mitt Romney by a 2-to-1 margin.

Democrats scoff at Labrador's suggestion.

"The only way this ends is when the speaker allows the full House to work its will," said Rep. Chris Van Hollen, D-Md., who took 63 percent of the vote in his last election. "We could pass a clean CR, to keep the government funded, today," he said, if Boehner would allow all House members to vote.

Thus far, Democrats have opposed Boehner almost unanimously, saying he has made no meaningful concessions. That leaves Boehner at the mercy of his 232-member GOP caucus, where conservative hardliners prevent him from passing any measure they oppose.

In past decades, congressional leaders often crafted bipartisan solutions in the political center to resolve tough issues. Then, however, more House members came from politically competitive districts. Taking a more centrist, cooperative stand often helped these lawmakers win re-election.

Now, far more House members come from firmly conservative or firmly liberal districts. Their only election vulnerability is in their party's primaries, when ideological purists might accuse them of being unacceptably cooperative with the other side.

The previous two government shutdowns, in the mid-1990s, ended fairly quickly. Many House members then faced greater threats in a general election than in a primary, because their districts were politically balanced. In 1995, for instance, 79 House Republicans represented districts carried by Democrat Bill Clinton in the previous presidential election, according to a National Journal analysis.

Today, only 17 House Republicans come from districts that Obama won.

The dramatic decline of House GOP moderates — who once came to Congress in big numbers from the Northeast and Midwest — was made clear this week when a supposed moderate insurrection drew only two votes against a Boehner-backed budget measure.

In a similar vein, moderate-to-conservative House Democrats, especially from the South, have virtually vanished.

The result is a House full of lawmakers confident in the rightness of their views, and in the likelihood of their re-election next year.

And therefore, no matter how many times the Democratic-controlled Senate rejects efforts to curtail "Obamacare," Republicans keep trying.

"We want them to admit there are problems with Obamacare," said GOP Rep. James Lankford of Oklahoma, where Obama won only 33 percent of the vote last year. As for how long the shutdown might last, he said: "I have no idea."