Editors' pick: Originally published July 15.

Earlier this week, Democratic presidential candidate Bernie Sanders finally endorsed Hillary Clinton.

The endorsement was a small ray of good news for Clinton, whose campaign has suffered through a difficult 10 days after FBI director James Comey called her use of a private email server while she was Secretary of State "extremely careless." Sanders said that it was important to defeat presumptive Republican nominee Donald Trump.

"I have come here to make it as clear as possible why I am endorsing Hillary Clinton and why she must become our next president," Sanders said at a joint rally in a Portsmouth, N.H. Tuesday. "Secretary Clinton has won the Democratic nomination and I congratulate her for that."

Clinton is banking on the support of a good portion of the more than 12.4 million voters who supported Sanders in the primaries. Sanders won 22 states and more than 1800 delegates. For the Democratic Party, the unified front distracted attention from growing concerns about its presumptive nominee's trustworthiness and could give it a boost in senate elections. The Democratic Party is hoping to take back the senate this fall. Still, the chemistry between the Sanders and Clinton on a stage at a high school gym suggests that the relationship between them will have to improve and that they will have to find firmer, common ground on major issues.

Sanders rarely glanced at Clinton during his roughly 30-minute address and never looked to hug her.

To be sure, Clinton has modified her stances on these issues but they remain unresolved in many voters' minds. But the perceived differences could hurt Clinton's chances in November. She's held a small lead over Trump nationally and in key swing states for the past few months but needs to convince Sanders' supporters to rally to her.

Clinton has already swung to the left on a number of points to lure Sanders voters appear in touch with the the country's populist tenor. She now comes closer to Sanders's positions on climate change, criminal justice reform and a $15-an-hour minimum wage. She's also nearer to him on the Trans-Pacific Partnership, an agreement signed earlier this year by the U.S. and 12 Pacific Rim countries to reduce trade barriers and enhance international commerce. Both oppose the pact, although Sanders more vehemently.

President Barack Obama and a cross section of Democratic and Republican lawmakers have strongly supported the agreement, although Sanders and a large, vocal group of opponents say that it would hurt American workers and businesses. Congress will vote on ratification later this year.

Still, these issues highlight the balancing act Clinton must maintain to ensure that she doesn't offend big business or labor -- two constituencies that she needs to win.

Consider below three other issues that present the same challenge, and may also be vexing for Sanders as he tries to remain a strong influence on Democratic policies.

1. The Millennial Vote

Sanders's success stemmed heavily from his ability to attract Millennials. This group of about 75 million strong between the ages of 19 and 34 related to his willingness to attack the status quo and to create a more equitable society. Milliennials tend to believe strongly in the importance of social responsibility. They are often less motivated than other groups by material rewards.

A Harvard's Institute of Politics (IOP) 2016 poll found that the 74-year old Sanders was the most popular candidate among voters in the 18-29 age group.

Clinton won't be able to match Sanders fiery rhetoric. She is a more traditional candidate with an uninspiring speaking style -- more comfortable discussing policy details in a quiet space making a speech before throngs. But she will have to lure in these voters through the strength of her arguments.

Sanders faces his own obstacles as a convention force. Some voters feel that his endorsement betrayed them. They say that a vote for Clinton is a vote for Wall Street not Main Street values.

2. Wall Street Reforms

Many Democratic voters have been repulsed by what they consider greed in the financial services industry. Throughout the campaign, Sanders repeatedly assailed big banks and proposed breaking up the largest ones. He said that the Dodd Frank Act of 2010, which was created to increase transparency and accountability in the financial services industry, has not been effective.

Clinton agreed with many of the key points in the legislation, and is sympathetic to some of the criticism of Wall Street, but she cannot afford to alienate an industry that has donated amply to her campaign.

Meanwhile, in recent weeks, Sanders has dialed back his remarks to the anguish of some of his supporters. His endorsement of Clinton offered fertile ground for a Trump tweet: "Bernie Sanders endorsing Crooked Hillary Clinton is like Occupy Wall Street endorsing Goldman Sachs," Trump wrote.

3. Campaign Finance

Throughout the primary, Sanders hotly criticized Clinton's fund raising. At one point, his campaign manager Jeff Weaver, accused Clinton of "looting funds meant for the state parties to skirt fundraising limits on her presidential campaign." Clinton's campaign said that this was unfounded. But the exchange highlighted the tension that campaign financing arouses.

Many Sanders supporters have been angered by the increasing role that campaign donations are playing in elections. They say that Clinton's reliance on sizable contributions from rich donors has made her beholden to their interests. They say that she is emblematic of a political system that favors the rich.

But the reality in a presidential election is that a candidate's ability to raise money greatly enhances his or her ability to win. Money allows a candidate to reach a wider audience. Clinton must appear sympathetic to the argument for campaign finance reform but not compromise her ability raise money. Both the Obama and Romney campaigns raised more than $1 billion in the 2012 election.