Politician in support of the motor car and the tube (4,5)

'the tube' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'politician in support of the motor car' is the wordplay.
'politician' becomes 'straw' (I've seen this before).
'in support of' is a charade indicator (letters next to each other) (in a down clue, some letters hold others up).
'the motor car' becomes 'jack' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'straw' put after 'jack' is 'JACK-STRAW'.

'and' acts as a link.

Can you help me to learn more?