The Senate could prove just as acrimonious and bogged down in 2011 as it was during the past 20 months, according to Capitol Hill players and political observers.

Republicans are more likely to predict a continuation — or an escalation — of the political food fighting that has characterized much of the 111th Congress, while Democrats, at least on the surface, will look to place more legislative responsibility on the GOP’s shoulders, in part to blame it for the gridlock likely to ensue.

“I think the Democratic agenda won’t necessarily change a ton; jobs and the economy will still be the first,” one Senate Democratic leadership aide said. “But what we’re able to achieve and how we will work with the Republican minority will be greatly on them.”

Republicans disagree and argue that much of the burden will rest with President Barack Obama and Congressional Democrats. They predict the midterm elections will serve as a referendum on White House and Democratic policies.

“This election is the equivalent of the voting public shouting ‘stop’ at the current Democratic leadership, regardless of whether they narrowly retain their majority or not,” a senior Republican Senate aide said. “It will be up to the Democrats to show they got the message if they remain in the majority. If by their actions they show they’re ignoring the public like they did on health care, the president likely will not win his re-election and they’ll lose their control of Congress in 2012.”

The Senate’s political tone in the 112th Congress will depend largely on what occurs in the midterm elections. Republicans are expected to gain seats, and the exact number will go a long way toward determining the level of partisanship in the second half of Obama’s term. How the president reacts, and how the Democrats respond, will also play a large role in the atmosphere.

For Republicans, it’s all about Obama. GOP Senate aides and Republican operatives who work off Capitol Hill said how they relate to the president is up to him. If Obama responds to the election by increasing his outreach and moderating his domestic agenda, bipartisan cooperation is possible, these Republicans said.

But should they perceive that the president is offering more of the same, Republicans will respond with more opposition than they have exercised since Obama took office in 2009, given the confidence, political strength and voter mandate they expect to accrue in the fall campaign.

“If we’re fortunate enough to have more Republicans in the Senate next year, it will likely be the result of a clear mandate sent by the American people. The path forward will stem from an acknowledgment by the president that government takeovers, sky-high spending, high unemployment and unsustainable debt is not the direction the American people want us to go,” a second senior GOP Senate aide said. “If that doesn’t happen, the president and his party in Congress will find a very serious, very committed Republican Conference that will be more than eager to drag them kicking and screaming into reality.”

Regardless, the next Congress is likely to see an end to the days when only moderates from either side of the aisle could dictate policy.

No longer will Maine Republican Sens. Olympia Snowe and Susan Collins decide whether any Democratic priority wins 60 votes to overcome a potential GOP filibuster. Instead, Democratic leaders will have to strike bipartisan deals or pick off large chunks of GOP votes to accomplish any legislative priority. And that depends on what the Republican caucus looks like and whether any members find it in their interest to work across the aisle, Democrats said.

“How Sen. McConnell manages his new caucus — knowing that there’s a need for more compromise, yet having more conservatives as a whole — is going to have an impact on what we get done,” the Democratic aide said about Minority Leader Mitch McConnell (R-Ky.).

On the Republican side, all eyes will be on conservative stalwarts such as Sens. Jim DeMint (S.C.) and Tom Coburn (Okla.), who could rise to new prominence with the likely election of tea party favorites such as Rand Paul of Kentucky and Joe Miller of Alaska.

Moderates in the Democratic ranks could find themselves as the primary contacts for bipartisan deals. Sen. Claire McCaskill (Mo.), one of several Democrats elected in 2006 on a pledge to shake up Washington, could rally a few Republicans behind a particular issue that then bubbles into a proposal on the floor. Or a grouping of perennial vote-sitters — such as Sens. Joe Lieberman (ID-Conn.) and Ben Nelson (D-Neb.), plus potential new additions such as Independent Gov. Charlie Crist, who is running for Florida’s open Senate seat — could form a loose alliance that proves influential during policy negotiations.

Retiring Sen. Evan Bayh (D-Ind.) tried to form a bipartisan caucus of moderates that fizzled shortly after its founding, and similar attempts in the past have proven unsuccessful. But with so many Democrats from the 2006 class looking to score a few legislative accomplishments as they vie for a second term in 2012, Capitol Hill prognosticators suggest the “rise of the moderates” story line has the potential to stick this time.

“They could decide who is in the majority and whether we get things done or not,” one senior Democratic aide said.