His defense attorney, Llorenç Salvà, confirmed that Chambers has donated over $1 million to humanitarian efforts in Gaza.
The legal action has drawn strong opposition from Spanish leftist politicians, including European Parliament representative Irene Montero, who urged Spain to reject the extradition.
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"Spain can't collaborate with Trump in the persecution of solidarity with Palestine: the government should protect him and not surrender him to Netanyahu's friends," Montero said.
In Spain's Congress, six members of the leftist Sumar party wrote a letter expressing concern that the extradition would set a dangerous precedent for political participation.
Trevor Aaronson, an author specializing in FBI and terrorism investigations, warned that the case reflects broader counter-terrorism policies being applied to domestic donors.
"All leftist groups are part of some huge network and are active participants in terrorism," Aaronson said, quoting the perspective of top counter-terrorism official Sebastian Gorka.
Aaronson compared the situation to the Holy Land Foundation case of the mid-2000s, where US prosecutors argued that humanitarian funds are fungible assets that indirectly benefit governing entities.
"School books in Gaza – that's more money that Hamas could then use for terrorism," he said.
This legal interpretation has historically discouraged charitable contributions to Palestinian causes due to fears of legal reprisal.
"A chilling effect, where no one wants to give money to Palestinian groups or to other left groups, because it could be used against them," Aaronson said.
Aaronson questioned the timing of the legal proceedings, noting that the humanitarian crisis in Gaza is currently at an unprecedented level.
"Arguably, the need for humanitarian aid in Gaza is greater than ever. Conflating that with terrorism is remarkable," he said.
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A Spanish court hearing to determine whether Chambers can be released on bail is scheduled for Thursday.
