Former Secretary of Housing and Urban Development and Democratic presidential candidate Julian Castro said Monday that his campaign needs $800,000 by the end of October or his run for president may be finished. 

"This is a critical moment – if my campaign can't raise $800,000 by Oct. 31, my campaign will be silenced for good," he tweeted. 

Castro, 45, is the only Latino in the primary and has long been considered a rising star within the party. The former San Antonio mayor has made immigration a central issue of his campaign platform, while facing a challenge on the issue from fellow Texan Robert "Beto" O'Rourke.

Castro in September had a somewhat controversial moment that might have hurt his support, when he seemed to have attacked rival Joe Biden for his age during a debate.  

Castro may also be concerned that he may not be able to qualify for next month's debate in Georgia, as he still needs to reach 3% support in four party-approved polls. 

New Jersey Sen. Cory Booker, another candidate in the race, faced a similar dilemma in September. He needed to hit a fundraising goal of $1.7 million to stay in the race, or else he would have to drop out. At the end of the month, he hit his fundraising goal and was able to continue his campaign. 

So far, Sen. Bernie Sanders of Vermont is the candidate raising the most money, with a haul of $25.3 million in the third quarter of 2019. Biden raised $15.7 million during the quarter, with Sen. Elizabeth Warren of Massachusetts bringing in $24.6 million.