Democratic Presidential candidate Hillary Clinton speaks at the Inaugural Barbara Jordan Gold Medallion at Texas Southern University on June 4, 2015 in Houston, Texas.Clinton received the Barbara Jordan Public-Private Leadership Award at Texas Southern University and in her remarks, urged swift action to restore the Voting Rights Act and replace the provisions struck down by the Supreme Court. She also spoke about the destructive impact of restrictive laws in states like Texas, Wisconsin, North Carolina, and Ohio that make it harder for voters to access the voting booth and cast their ballots.
Hillary Clinton calls for voting rights expansion
04:04 - Source: CNN
Denver CNN  — 

Hillary Clinton’s campaign manager had one message for her top supporters ahead of her kick off next week: We now have three opponents, so keep your focus on the primary.

In a memo obtained by CNN from a recipient, Robby Mook, the campaign’s manager, told supporters that while they now have “more than 11,000 active volunteers in all 50 states,” the Democratic side is not going to be a cakewalk.

“The field is competitive,” writes Mook in a memo titled, “The Next Phase of the Campaign.” “In the last two weeks alone, we have seen three new candidates enter the Democratic primary. And polls show that our party wants that competitive primary.”

Mook adds that “Becoming the Democratic nominee is never easy. Nor should it be.”

“Voters and caucus-goers want to know their candidate is tested and ready to represent their values and priorities in the general election,” Mook writes in the memo that was sent Tuesday afternoon. “While we know all that Hillary has done in her life to stand up for our families and our country, we also know that she’ll have to work hard to earn every vote and every delegate.”

Clinton announced her presidential campaign in April, but will hold her official kickoff and first rally Saturday in New York City. Following her speech, the presidential hopeful will pick up her campaign’s pace and hit the first four nomination states – Iowa, New Hampshire, South Carolina and Nevada - in a week. She will also hold a series of fundraisers across the country.

Since Clinton announced her campaign, former Maryland Gov. Martin O’Malley, Vermont Sen. Bernie Sanders and former Rhode Island Gov. Lincoln Chafee have all announced they will challenge Clinton for the nomination.

Campaign aides have long said that they expected a challenge, but Tuesday’s memo is the first time Clinton’s campaign manager has bluntly set expectations with supporters.

“In the coming months, poll numbers will shift up and down and expectations will be set too high and too low,” Mook writes. “We will remain focused on communicating Hillary’s vision and working with you to build our operation on the ground.”

Clinton has recently experienced a dip in the polls, while Sanders – her most strident opponent so far – has seen a bump, coupled with sizable turnout to events in early states.

RELATED: Hillary Clinton ekes out slim win against Sanders in Wisconsin straw poll

A CNN/ORC poll released earlier this month found that more people have an unfavorable view of Clinton now than at any time since she was a senator in 2001. Despite the fact that Clinton remained dominant against her Democratic challengers, a growing number of people said they feel Clinton is not honest and trustworthy.

Joel Benenson, Clinton’s pollster, told CNN that he takes “all these public polls with a grain of salt.”

Since kicking off her campaign, Clinton has raised only primary dollars, a fact her campaign highlights as evidence she is “taking nothing for granted.” But, at times, campaign aides have had to catch themselves when they describe the coming campaign as a 16 month fight, an assumption that Clinton will win the nomination.

Mook does not only focus on Democrats in the memo.

“We must expect more desperate attacks from the GOP,” he writes. “The Republican field grows every day with a variety of new candidates with two things in common: they are all out-of-touch with everyday Americans and they all have offered little more than attacks on Hillary Clinton.”