I don't think the top politicians in each country had to sign off on this. More likely the money was already allocated to scientific research and there were people in charge of deciding how to spend it.
<cynical rant>To the extent that politicians did have to be persuaded, they were probably persuaded by other means than that of elucidating the potential scientific payoffs. They were probably persuaded using political arguments, i.e. how it would play with their voters. Politicians are not, in practice, guardians of a sacred trust. They operate by their own rules and for their own reasons.</cynical rant>
<cynical rant>To the extent that politicians did have to be persuaded, they were probably persuaded by other means than that of elucidating the potential scientific payoffs. They were probably persuaded using political arguments, i.e. how it would play with their voters. Politicians are not, in practice, guardians of a sacred trust. They operate by their own rules and for their own reasons.</cynical rant>