An internal memo from the campaign of former Vice President Joe Biden said it's "nearing impossible" for Sen. Bernie Sanders, I-Vt., to regain the lead in delegates after losses in several of the Democrats' presidential primary contests.

The memo said the campaign netted 160 delegates, including up to 80 won on Tuesday. Biden campaign officials said they expected his lead to expand in "some of our strongest" states -- Arizona, Florida, Illinois, Ohio and Georgia.

"Of 682 delegates awarded in those states, conservative estimates have us winning more than 400 delegates and netting more than 150 delegates," the memo read.

SANDERS VOWS TO PRESS ON WITH PRESIDENTIAL CAMPAIGN AND PRESS BIDEN ON PROGRESSIVE ISSUES

The officials said wins for Sanders in Vermont, Colorado and Utah haven't collected him enough delegates to be able to compete.

"It's not just that Sanders has failed to win a large number of states, it's also that these wins have not netted significant delegates for him in the way they have for us," the memo read.

"Should our broad base of support remain -- and we have seen no signs that would indicate otherwise -- it will be nearly impossible for Sanders to recoup his current delegate disadvantage," it continued.

Sanders fell further behind Biden following losses in Michigan, Missouri, Mississippi and Idaho during this week's contests. The populist candidate, however, has vowed to press on with his White House bid.

"Last night, obviously was not a good night for our campaign, from a delegate point of view," Sanders said Wednesday while speaking to reporters from Burlington, Vt.

He then pledged to see his rival at Sunday's debate in Phoenix.

CLICK HERE FOR THE FOX NEWS APP

The memo said attacks from Sanders on Biden's positions on trade and social security have had little impact. It cited support from suburban, and college-educated voters as well as union households.

"Turnout was up among the voters and in the states where we performed best," the memo read. "These are the kinds of states and voters who will deliver a victory in November."