Hillary Clinton sits in on a round table discussion as she visits the Kikis Chicken and Waffles restaurant on May 27, 2015 in Columbia, South Carolina.National Journal

BROOKLYN, New York—If you look out from one side of Hillary Clinton's campaign office here, you can see straight to the Brooklyn Bridge and lower Manhattan, with no apartment buildings or office towers blocking the breathtaking views.

Clinton's path to the Democratic presidential nomination looks only slightly more obstructed, even as the field of candidates opposing her filled out this week. Vermont Sen. Bernie Sanders, the self-described socialist who formally began his campaign with a rally Tuesday, and former Maryland Gov. Martin O'Malley, who plans to officially join the race Saturday, each face a mountainous climb to overcome her many advantages. And yet Clinton's response to them could still color her White House hopes.

As Sanders and O'Malley enter the race, Hillary Clinton's campaign says flatly it is determined to avoid a bidding war for support of the party's energized liberal base. That won't be easy with both men hoping to create contrasts by advancing cutting-edge liberal positions. The choice confronting Clinton is how far to move to preempt her rivals' ideas without allowing her opponent in the general election, if she gets that far, to portray her as extreme or unprincipled. In both parties, previous front-runners from Al Gore (on gun control) to Mitt Romney (on immigration) have slipped off that tightrope, with painful consequences, even against primary opponents they ultimately dispatched fairly easily. Clinton faces the same risk.

Clinton already has staked out left-leaning positions on key social issues, including gay marriage, immigration, and criminal justice reform. On these questions, she has embraced more liberal ideas than her husband Bill Clinton did during his presidency. But the center of opinion among Democrats—and the country—has shifted left on almost all of these cultural questions since the 1990s. With good reason, Clinton's camp is confident that her cultural positioning rests on solid ground with not only Democrats, but also the broader electorate.

The bigger question is where Clinton lands in her economic decisions. Her early rhetoric has stressed income inequality more than Bill Clinton's ever did. But she has not yet revealed much about her actual economic agenda, or definitively staked her place on the continuum between her husband's business-friendly "New Democrat" centrism and the populism associated with Sen. Elizabeth Warren.

On this front, O'Malley and Sanders have planted their flags with Warren. Both have condemned the Trans-Pacific Partnership trade agreement President Obama is laboring to complete. Both have spoken favorably of raising the national minimum wage to $15 per hour. In virtually identical language, each has called for breaking up the nation's largest financial institutions. O'Malley also wants to restore the "Glass-Steagall" wall between investment and commercial banking dismantled under Bill Clinton. Both would expand Social Security benefits.

Both candidates also oppose the Keystone Pipeline, and Sanders has sponsored legislation to impose a tax (with consumer refunds) on the carbon emissions linked to global climate change. Sanders has also proposed a $1 trillion infrastructure initiative, and a plan to allow all students to attend public college tuition-free that would be funded by a financial transaction tax. Though O'Malley also stresses government efficiency and reform, both of these agendas would massively expand Washington's size and reach.

That's where O'Malley and Sanders will present Clinton the most consequential choices. While liberal activists correctly note that many of these individual policies poll well—and surveys show persistent concern that the economy now favors the wealthy—Americans also consistently express skepticism about excessive government. Clinton's danger is embracing an agenda so bloated with expensive promises that it allows Republicans to caricature her as a return to intrusive, big-spending government policies that still face public resistance.

Her aides say they recognize that risk. "A lot of these issues are core concerns for her," says one senior campaign adviser. "We need to be in that space and make our case "¦ But that's a different concept than saying you have to go left of either of them. I don't know that an arms race is what is going to help her here." Clinton may have foreshadowed her broader approach when she recently urged "making college as debt-free as possible." Those qualifying final two words separated her from Sanders' pledge of tuition-free attendance by about the distance between lightning and a lightning bug. Relevance, not equivalence, seems the Clinton watchword.

Veteran Democratic consultant Joe Trippi, who ran Howard Dean's liberal insurgency in the 2004 Democratic presidential contest, says it's unclear if Sanders and O'Malley can attract enough support to force Clinton further in their direction. Their task, he adds, is complicated because many activists will temper their demands on Clinton because they fear losing the White House while Republicans already control Congress and most state governments. "The feeling is, we don't have the luxury to get everything we want, to get that perfect purity," Trippi said.

The Democratic primary electorate has grown more liberal since Bill Clinton's era, as Millennials and minorities have replaced blue-collar and older whites who have shifted into the GOP. Hillary Clinton's challenge is to respond to that current in the primaries without getting carried to ground she cannot defend if she reaches the general election.

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