WASHINGTON - Barack Obama's presidency has been a wild ride for the U.S. Congress and lawmakers are bracing for more turbulence when they begin returning on Monday to tackle an array of tough issues from healthcare to energy.

In the three months since Obama took office, his fellow Democrats in Congress have overcome Republican objections and unleashed a raft of spending to try to buoy the sinking economy.

With the Senate coming back on Monday and the House in on Tuesday, following a two-week recess, the Democratic leadership in both chambers will press its advantage, while undeterred Republicans dig in their heels.

Now the agenda gets more ambitious, and by definition more contentious, said Andrew Taylor, chairman of the political science department at North Carolina State University, noting Democrats may have trouble within their own ranks over some of the most ambitious spending proposals.

The whole notion of deficits is going to make some Democrats uneasy, Taylor said.

Democrats take heart from polls that show Obama remains highly popular and the public has more confidence in Democrats than in Republicans to solve the nation's problems.

Yet there is no sign Republicans, who opposed Obama's $787 billion economic stimulus package and $3.5 trillion budget plan, are about to cooperate with what they denounce as Obama's liberal tax-and-spend policies.

Instead, they see a political opportunity -- and last week aired a television and radio ad campaign targeting 43 potentially vulnerable House Democrats who they accused of endorsing a reckless spending spree.

The Democrats are in largely conservative districts, which had close elections in 2008 and could tip to Republicans in the 2010 midterm vote.

We will continue to hold these Democrats accountable for rubber-stamping (House of Representatives Speaker) Nancy Pelosi's agenda that will burden middle-class families and inflict further damage on an already fragile economy, said Ken Spain of the House Republican campaign committee.

SENATE BATTLEGROUND

Democrats, who extended their control of Congress in the 2008 elections, can ram a bill through the House on a majority vote. They may face increased problems in the Senate where they need 60 votes in the 100-member chamber to clear Republican roadblocks.

With 58 votes now, Democrats need at least a couple of Republican senators to hit 60. They won over three to help pass Obama's stimulus plan, but one of them -- Pennsylvania's Arlen Specter -- faces a tough re-election challenge and may be reluctant to cross party lines again on some issues.

One of the first agenda items will be Senate consideration of a bill backed by Democrats and some Republicans to tighten laws against financial fraud.

At stake on other fronts are some of the chief policy goals of the Obama administration, including its plan to restructure the U.S. healthcare system and to cut U.S. emissions of carbon dioxide and other pollutants blamed for climate change.

Some Republicans say they are willing to talk -- but only if the Democrats play ball.

It can happen, but they have to get together with people like me. It's uphill. It's very complex, said Republican Senator Orrin Hatch.

An early test will come when House and Senate negotiators work to resolve differences between the budget plans, each totaling about $3.5 trillion, that their chambers approved for the new fiscal year that starts on October 1.

One point of contention will be whether to include provisions that would enable Democrats to fast-track legislation to overhaul healthcare -- a move Republicans oppose but may be unable to stop.

ECONOMY WILL DECIDE

Political analysts say poll results showing public support for Obama's economic agenda strengthens the Democratic hand in the short term.

The polls give Obama the ability and leverage to say no to criticism that he's doing too much too fast, said Ethan Siegal of the Washington Exchange, a private firm that tracks Washington for institutional investors.

Republicans have been looking for political traction and last week helped back a national series of tea party anti-tax protests they hope will help their party's bid to be seen as a fiscally responsible alternative to Obama's Democrats.

House Republicans share the American people's frustration and are proposing better solutions, House Republican leader John Boehner said in a statement supporting the protests.

While Republicans are now on the defensive, Obama and Democrats will be warily watching the economy.

If the economy turns around, which it cyclically should do close to the 2010 election ... then these cat fights over healthcare, energy and education aren't going to make a difference, Siegal said.

If the economy doesn't turn around, (voters) are going to remember it was bad when Obama came in and he has done nothing for me and therefore I'm voting Republican.

Healthcare Energy Pennsylvania Nancy Pelosi