Optimists might think twice before seeing Congress’ bipartisan agreement to keep the government running another year as a road map for 2015.

The dynamics that tamed both parties’ ideological wings on the weekend will change next year, handing new challenges to congressional leaders who often struggled just to keep the government’s bills paid. Republicans will feel new pressures to show they can produce, even as 2016 presidential politics, and President Barack Obama’s incentives to veto legislation, add uncertainties to the mix.

On the bright side — for people who abhor government gridlock, at least — last week’s events showed that lawmakers can assemble bipartisan majorities in the political center on big measures that leave everyone a bit unhappy. The $1.1 trillion spending bill will finance most of the government through September, making a repeat of the 2013 shutdown unlikely.

The bill angered conservatives who wanted to block Obama’s executive changes to immigration policy. And it displeased liberals who say it unwisely loosens restrictions on risky Wall Street practices.

But Obama and most congressional leaders called it an acceptable compromise, the type of accord once common in Washington. The only top congressional leader to oppose it was House Democratic leader Nancy Pelosi, and she stopped short of pressing her colleagues to kill it.

The Senate will be in a session a few more days to deal with tax breaks, nominations and terrorism insurance. When the new Congress convenes next month, four important changes will occur. They don’t make bipartisan accords impossible, but they will pose new complications:

—Republicans will control both legislative chambers, not just the House. This enhances their clout, of course. But it also will encourage some conservative firebrands to demand politically unfeasible goals, such as repealing the president’s health care law.

—Senate Democrats will use the same filibuster rules to block GOP measures that Republicans have used for six years. Republicans will hold 54 of the Senate’s 100 seats. Measures being filibustered need 60 votes to advance.

—Obama may decide to veto some bills that Congress passes. Overriding vetoes is extremely difficult, requiring two-thirds majorities in the House and Senate.

—The 2016 presidential race, now underway, will complicate congressional politics. As many as five senators are considering joining the race. They include Republican Ted Cruz of Texas and Democrat Elizabeth Warren of Massachusetts. Both tried to derail the big spending bill for different reasons.

Republican Sen. John McCain of Arizona, the party’s 2008 presidential nominee, told CBS’s “Face the Nation” on Sunday: “Unless we can show the American people that we can govern, then we’re not going to elect a Republican president in 2016.”

But it won’t be easy, said Ron Bonjean, a former top GOP congressional aide. Even with Republican House and Senate majorities, he said, the GOP agenda “could grind to a halt in the Senate because it will take 60 votes to pass anything.”

Republican Sen. Mitch McConnell of Kentucky, the incoming majority leader, says the Senate will accomplish more because he will allow wider debate and more amendments to bills, which Democrats had sharply limited. He says Republicans are willing to make tough votes, even on Democratic amendments designed for political mischief.

“Partisanship itself has never been the problem,” McConnell said in a statement Sunday. “The real problem has been a growing lack of confidence in the Senate’s ability to mediate the tensions and disputes we’ve always had.”

Former Democratic Senate aide Jim Manley says it won’t be that simple. The conservative-dominated House, he said, “will send one bad bill after another to the Senate,” putting McConnell in a bind. “It will either die in the Senate” thanks to filibusters, Manley said, “or by presidential veto.”

Compromise and accomplishment will remain difficult in the next Congress largely for the same reasons they’ve been difficult in recent years. The nation and the political parties are increasingly polarized. Congressional moderates in both parties have been driven from office, and many House members owe their election to hard-core liberal or conservative activists who dominate the nominating primaries.

Democratic Rep. John Sarbanes of Maryland, whose father, Paul, spent 30 years in the Senate, said it will be “very hard” for Congress to return to the more accommodating practices of his dad’s era. He said lawmakers are under relentless pressure to raise campaign money, and when they face a policy question, they wonder, “what would my money patrons think if I were to give ground on this provision?”

“That tends to put members of Congress in a harness,” Sarbanes said.

(AP)