Washington (CNN) The battle lines for the 2018 midterm election are being revealed as both parties gear up for emotional debates on issues and positions that were one confined to the radical fringes but now drive American politics.

Republican fratricide is looming in a clash between Donald Trump's populist, economic nationalism and Washington governing elites compered by Steve Bannon and shows the GOP's destructive 2016 primary did nothing to solve its deep philosophical splits.

Democrats are tracking left toward their progressive base, as the long list of 2020 potential presidential hopefuls line up behind Bernie Sanders and a single payer health care plan.

The positioning, just 14 months before a midterm election that could reshape the Trump era, is a sign of a volatile political environment still reverberating from the consequences of the President's victory last year, and the progressive crusade by Sanders that Hillary Clinton blames in part for her defeat.

And it's a signal that partisanship is likely to become even more extreme in the years to come, making the assignment of providing effective and consistent governance, that has proved beyond both parties, even more challenging.

Bannon For America?

Republicans always knew that 2018 was going to be a tough year -- first-term incumbent presidents and their parties traditionally get a lashing from the voters. But the GOP's hopes of holding the House and expanding its majority in a favorable set of Senate races are being threatened by internecine conflict.

Increasingly, Trump, the Republican President, has seemed to be running against his own Republican Party, fulminating at its leaders for failing to pass his agenda and feuding with individual lawmakers who criticize him. His deal on a short-term funding package and lifting the debt ceiling with Democrats last week only fueled questions about his loyalties.

Now, his erstwhile political guru Bannon, styling himself as a "street fighter," is eying up a roster of GOP primary challengers more in line with Trump's establishment-busting creed than the senators and dwellers of the Washington swamp who currently occupy Republican seats.

It's a high-risk strategy, since some senior party figures fear that a desire to punish senators insufficiently loyal to Trump in primary races could deliver candidates who are less well-placed to defeat Democrats.

But Bannon is warning that departures from the themes that won Trump the presidency, for example, help for undocumented migrants brought to the US as children after the President canceled the DACA program, risk alienating the party from its base and could detonate at a vital moment of the political calendar.

"If this goes all the way down to its logical conclusion, in February and March, it will be a civil war inside the Republican Party that will be every bit as vitriolic as 2013," Bannon said. "And to me, doing that in the springboard of primary season for 2018 is extremely unwise."

A source close to Bannon told CNN that he is preparing to back primary challengers against Republican senators including Roger Wicker in Mississippi, Bob Corker in Tennessee and Dean Heller in Nevada, as well as Jeff Flake, a vehement Trump critic, in Arizona.

Interventions by Bannon could introduce a powerful, disruptive element to Republican primary races, especially if he is funded by his wealthy backers in the Mercer family and given his ability to inject populist rhetoric into the bloodstream of the Trump base through Breitbart News, where he returned after leaving the White House last month.

Competitive primaries could also force Republican bosses to divert attention and resources away from efforts to unseat incumbent Democratic senators and the effort to cling onto the House, where GOP worries are being exacerbated by a growing list of retirements of veteran lawmakers.

"I do get the fact that Bannon wants to help the President," said Ford O'Connell, a Republican political strategist.

"I get the fact that a lot of folks who support the President are frustrated with more mainstream members of Congress who are not pushing the Trump agenda through," he added. "That said, this could wind up being potentially disastrous. It's one thing to challenge a candidate but if you can't field a challenger who can win in the general election that is absolutely not helpful."

JUST WATCHED Bannon: GOP wants to 'nullify' 2016 election Replay More Videos ... MUST WATCH Bannon: GOP wants to 'nullify' 2016 election 00:47

Where can Bannon win?

Bannon's influence and spending power could be particularly effective in a state like Mississippi, where Sen. Thad Cochran endured a grueling primary challenge from state Sen. Chris McDaniel, a Tea Party hero, in 2014. McDaniel may have Wicker in his sights next year.

"In a state like Mississippi, our media markets are less expensive than other states. Money goes a long way," said an experienced Magnolia State Republican operative, speaking on condition of anonymity to frankly discuss the dynamics of a potential primary race. "If he were to target Sen. Wicker and Mississippi with a lot of money, that could be a problem."

Republican Party leaders will watch Bannon's effort especially closely to see whether it is being coordinated with the President himself. Trump has already inserted himself in the Arizona race, slamming Flake, who wrote a highly critical book about the President's political movement.

But significantly, when Trump traveled to the state for a rally recently, he did not specifically endorse Kelli Ward, who is planning to challenge Flake, and is seen by many Republican leaders as a GOP candidate who could lose to a Democrat.

Trump's legislative director Marc Short could not give a guarantee Tuesday that the President would agree to support all incumbent Republican candidates.

"I don't know that the President has a commitment to avoid primary processes. Each one will play out by itself," said Short at a Christian Science Monitor breakfast.

JUST WATCHED Clinton lays blame on Sanders in new book Replay More Videos ... MUST WATCH Clinton lays blame on Sanders in new book 01:44

Democrats flock to Sanders' ideas

While Republican internecine warfare deepens, Democrats are showing signs of emerging from the trauma brought on by Clinton's defeat. The debt ceiling deal crafted last week by Trump, Senate minority leader Chuck Schumer and Nancy Pelosi, leader of the Democrats in the House, gave the party a boost, as it was seen as outfoxing Republican leaders Mitch McConnell and Paul Ryan.

A clutch of Senate Democrats who may have ambitions of running for president in 2020 are meanwhile lining up to co-sponsor Sanders' bill calling for a government-run health care system for all that will be unveiled Wednesday.

The moves by senators like Kamala Harris, Cory Booker, Elizabeth Warren and Al Franken , suggest a leftward shift in the party since it appears that potential national candidates now believe that it is more of a risk to be seen as opposing state-run health care than for it. The issue looks certain to become a litmus test for future presidential candidates.

"If you look at the traction of the single-payer issue, anyone running for office in 2018 for 2020 would need to spend a lot of time understanding (it)," said Tharon Johnson, a Georgia political consultant who ran President Barack Obama's southern states operation in his 2012 re-election bid.

Trump's failure so far to repeal and replace Obamacare means that questions around "health care are going to be front-and-center for both parties," Johnson said.

Still, it is not clear whether focusing on single-payer schemes is a sure-fire winning argument for Democrats in national races. And its emergence could be used as a cudgel against Democrats running for re-election in red states.

Democratic Party leaders on Capitol Hill are treating the issue gingerly.

Steny Hoyer, the House minority whip, distanced himself from the Sanders plan on Tuesday, saying it was only one approach being considered by Democrats.

Calls by Sanders last year for universal health care in his primary campaign frequently exasperated Clinton, who portrayed herself as running a solutions-based campaign in the real world of what could get done in Washington.

On Tuesday, promoting her book about the election "What Happened," Clinton gave voice to some of that frustration.

She told the "Pod Save America" podcast that she had no "criticism whatsoever in staking a big claim on where we need to end up," but added: "I also say, look let's be realistic about how we are going to get to where we need to be."

But for now, with the possibility still distant that the party may win the power to take on the mammoth task of health care reform, it's not surprising that ambitious Democrats are choosing aspiration over practicalities.