The First Circuit has determined that in a 236(a) bond hearing, the Department of Homeland Security bears the burden of proving the detainee is a danger to the community and a flight risk. With respect to danger, the burden is clear and convincing evidence. For flight risk, the burden is preponderance of the evidence. The court determined that this burden allocation is required by the Due Process Clause of the Fifth Amendment.
The full text of Hernandez-Lara v. Lyons can be found here: