How does a President's endorsement truly affect a political campaign?

Breaking news across the United States in almost all major political media has been Barack Obama's endorsement towards Hillary Clinton's Presidential campaign. What does this mean for her, the democratic party, and the presidential race overall? Barack Obama won the Democratic nomination in 2008 over Hillary Clinton, so, not only is he endorsing his former competitor, he is also endorsing the current winner of the Democratic nomination. His endorsement is extremely important, especially by influencing how the general public will view her as the next possible president. Obama may not have been able to achieve everything he promised, but we all know that being President is not an easy job. The fact that he admits this by saying, "I know how hard this job can be. That's why I know Hillary will be so good at it," is not only major compliment to her, but also what can be seen as proof of her character and work ethic (Washington Post). She has worked by his side for the past 8 years as his Secretary of State, so this is not a comment to be taken lightly. In addition to this, he spoke to Bernie Sanders and as a result, Sanders has stepped aside and Hillary now has the spotlight in this increasingly dramatic Presidential race against Trump.