Obama is providing jam today, and spinach tomorrow, said Gillian Tett of The Financial Times on the Radio 4 Today programme this morning (4:14 mins into this extract). She was referring to his new job-creation measures announced recently.
'Jam today' is a twist on the original expression 'jam tomorrow' which refers to something pleasant that is promised, but that will never materialise. The original phrase comes from the book Through the Looking-Glass, and What Alice Found There, the sequel to Alice's Adventures in Wonderland. The White Queen tells Alice "The rule is, jam tomorrow and jam yesterday - but never jam today" (Carroll hyphenated tomorrow [to-morrow] and today [to-day]).
The phrase captured the public's imagination and soon other 'jam' phrases were being coined eg 'you want jam on it, too?' said if someone expected too much, and 'money for jam' ie easy money.
Tett was creative with the phrase this morning on the radio to evoke a strong image. The 'spinach tomorrow' addition is her own idiosyncratic creation. Perhaps she doesn't like spinach. More likely the allusion is to green vegetables, commonly disliked by many children and some adults.
The phrase 'jam tomorrow' is so well known that people can easily make puns on it or use the word 'jam' in other phrases and know that the allusion will be understood. In the 1960s the Labour politician Tony Benn made the comment "Some of the jam we thought was for tomorrow, we've already eaten" (from The Oxford Dictionary of Phrase and Fable, 2006 edition).