Democratic presidential candidate Julian Castro announced to his supporters that, if he does not raise a substantial amount of donations, he will have to end his campaign.

“I’m extremely proud of the historic and bold campaign we have built together,” Castro tweeted Monday. “But this is a critical moment — if my campaign can’t raise $800,000 by October 31st, my campaign will be silenced for good. Help us keep up the fight.”

The tweet linked to a donation page for Castro, where the candidate explicitly says he will “have no choice” but to end his presidential campaign if he can’t raise $800,000 by the end of the month.

The most recent FEC filings show his campaign only had $672,333 cash on hand at the close of September. His campaign raised $3,495,406 and spent $3,960,970 last quarter. Top-tier Democratic presidential candidates such as Elizabeth Warren and Bernie Sanders, on the other hand, have tens of millions of dollars at their disposal.

A surge of donations, Castro’s campaign says, is needed in order to make it on the next presidential debate stage.

Castro has already reached the 165,000 donor threshold necessary to qualify for the November Democratic debate, but he has not been doing well enough in the polls. DNC rules mandate that qualified candidates must hit at least 3% in four different polls to make it on the November stage. Castro needs more cash to fund campaign activities and raise his profile among Democratic voters.

So far, the beleaguered candidate has barely polled above 1%. The Real Clear Politics aggregate of nationwide surveys shows Castro polling at an average of .8%, a far cry from Joe Biden’s 29.2% or Warren’s 23.4%. A newly-released survey of Iowa voters, who are the first in the nation to hold a presidential primary, showed Castro polling at 0%.

“The truth is, for our campaign, these debates have offered our only guaranteed opportunity to share my vision with the American people. If I can’t make the next debate stage, we cannot sustain a campaign that can make it to Iowa in February,” Castro wrote in an email to supporters. “My presidential campaign is in dire need of financial resources to keep going.”

Castro, who served as the Housing and Urban Development secretary under the Obama administration, has made immigration his signature campaign issue since entering the presidential race. (RELATED: Julian Castro Leads LGBT Migrants To US Border)

The former San Antonio mayor wants to decriminalize illegal immigration, including the decriminalization of illegal re-entry, which is a felony under U.S. law. He also pledged, if he’s elected to the White House, he would immediately end President Donald Trump’s Remain in Mexico program, which has kept thousands of asylum seekers from entering the U.S. before their claims are processed.

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