Stars of the new George Bush film, W, backed Barack Obama to succeed him when the movie premiered in London.
Josh Brolin, who plays the current US president, said: "I would say Obama for sure."
Director Oliver Stone added: "I would vote for Obama, he's a reformer."
Elizabeth Banks, who plays the president's wife Laura, said she is a registered Democrat and saw no reason not to support the party's candidate.
But Stone stressed that the film was not anti-Republican propaganda, despite his personal endorsement of Mr Obama.
"It's a great story. This guy changed history. We underestimated him," he said of Mr Bush.
"He took over the world stage and pushed the extremists' buttons."
Stone said Mr Bush "had left us in a dark hole" but his intention was for people to watch W (pronounced dubya) and understand more about the man and how he became president.
The film follows the young Mr Bush and shows him meeting Laura, becoming president and eventually taking the decision to invade Iraq.
Brolin said he had initially turned down the lead role.
"I didn't understand what he (Stone) was going for. I thought Oliver had an agenda," he said.
"It wasn't until I read the script that I realised it was a brilliant character study."
Brolin, whose performance has received critical acclaim, said: "I went into a five-month black-out and did all the study I could."
British actress Thandie Newton was among the stars who braved the rain at last night's premiere at the Odeon, in Leicester Square.
Newton, who plays US Secretary of State Condoleezza Rice, said: "I admire her discipline. What she has chosen to do with it I'm less in awe of."
The actress said she hoped the film would help people make decisions that "will be of benefit to the planet".