No candidate in decades has been in as strong a position to win a major-party nomination as former Secretary of State Hillary Rodham Clinton. Not since Richard Nixon in 1960 breezed to his appointment with destiny in Chicago has a presidential contender had so easy a time advancing to the finals in presidential politics.

Which is not to say that there is clear sailing ahead for Ms. Clinton, whose strong position may be more attributable to her lack of opposition than to her lack of vulnerability. She still has a hard trial ahead — difficult political obstacles, troublesome alliances, vitally important choices. Here are some of the challenges that may be keeping her advisers up at night — or should be:

• Continue to build a firewall in the South but concentrate on Iowa and New Hampshire.

There’s little doubt right now that she’ll be the nominee, but it isn’t in her interest to permit a protracted struggle to develop against Sen. Bernie Sanders, whom no one but his extremely devoted supporters believe will be crowned at the Democratic National Convention in Philadelphia.

Yet there is a real possibility that the left-leaning caucus constituency in Iowa and the region-conscious voters in New Hampshire will continue their strong support for the Vermont senator in the two earliest tests.

History shows us that in these early contests it is not so much results as perceptions that matter; take 1972, for example, when Sen. Edmund S. Muskie won the New Hampshire primary but performed under the experts’ expectations. Ms. Clinton must beat expectations in Iowa and New Hampshire and thus clear the field for herself for the rest of the winter and spring.

Many Democratic strategists believe her last campaign, against Sen. Barack Obama of Illinois, suggests that a protracted nomination fight doesn’t necessarily hurt the party’s eventual choice. But 2016 is not 2008, when Ms. Clinton’s presence in the race made Mr. Obama seem more moderate, rendering him more appealing to independents and Republicans in November. This time, Ms. Clinton is facing an opponent who seems intent on forcing her to the left, especially on economic issues relating to income inequality. Many dangers lurk there for her.

So it’s especially important for her to curtail this nomination fight. Otherwise she will face uncomfortable occasions to prove herself, unnecessary places to spend down her campaign treasury and unwanted challenges like the ones that follow . . .

• More than any other presidential candidate, she must have a strong position on terrorism.

This is an irony, given that she is the only candidate in both parties who has real experience in foreign policy. But this is a case where strength also may be a liability; her Republican rivals will pillory her for the Benghazi episode in particular and for her views on Libya in general. They will argue that it was the foreign policy she designed and prosecuted that created America’s vulnerability today.

Though she eventually issued a strong statement late last week that went beyond the president's policies, her first instincts were not promising. Emphasizing her experience with the terror attacks of 2001, for example, plants her in the past while many of the Republican contenders were not even in national politics in that era. Sen. Marco Rubio, for example, hadn’t even completed his second year in the Florida House and was five years away from becoming speaker. Sen. Ted Cruz of Texas was in the Bush Justice Department and was a dozen years away from elected office.

The equivalent of Ms. Clinton speaking about the 2001 attacks would be for Dwight Eisenhower to have talked about Pearl Harbor in a year that would bring the Suez crisis and the revolution in Hungary. For Gen. Eisenhower as for Ms. Clinton, those were different eras entirely.

• She must clarify her posture on, and relations with, Wall Street.

The common wisdom is that Ms. Clinton’s greatest danger ahead involves her emails. But that may not be so. Her greatest danger ahead may be her profile as a plutocrat cozy with the mandarins of finance.

Ms. Clinton argued this month that Mr. Sanders had unjustifiably attacked her integrity by suggesting she was a captive of her contributors. Only in office will we know the answer for sure. But in a way Ms. Clinton is a political captive of those contributors, and Mr. Sanders will not be the last one to make that charge.

His critique might be dismissed as the prattling of an inconsequential figure who gets attention only because he is the only person standing between her and a coronation for the presidential nomination. But no one listening to the debates among the Republicans — the ones who used to represent big business and finance — can doubt that their nominee will mount a populist campaign against Wall Street and against Ms. Clinton. She can be sure that Mr. Cruz and Mr. Rubio already have their applause lines.

• Though it seems premature, she must think about a running mate.

Usually this is a fanciful parlor game, but the lack of real competition in the Democratic race and the lack of credible, nationally known potential vice presidents in the Democratic Party make this a real imperative.

This conundrum underlines the irony of the Democratic position in 2016. The party has all the demographic factors going for it — great appeal among youth and solid strength among blacks and Hispanics who are increasingly important factors in the American electorate, especially in the big states. And yet the Democratic race is between a white woman who just turned 68 and her distant rival, a white man who just turned 74. The governor of the biggest state is a Democrat who once was a big-city mayor (Oakland) and a state attorney general, and anyone with that profile ordinarily would be a strong vice-presidential candidate. But Jerry Brown will be 78 at the Philadelphia convention.

The result is that there are few Democrats who come to mind as potential vice presidents. The usual repository of running mates are the governors, where the Democrats have only 18, and the Senate, where the Democrats account for 46, including independents. Before the spring is out, one of those independents, Sen. Angus King of Maine, a former governor, may attract Ms. Clinton’s attention. So might Gov. John Hickenlooper of Colorado, a former mayor of Denver. But as Dan Quayle and Spiro Agnew prove, it’s not easy to pick running mates correctly.