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

'the tube' is the definition.
I know nothing about this answer so I cannot tell whether this works.

'politician in support of the motor car' is the wordplay.
'politician' becomes 'straw' (I've seen this before).
'in support of' says to put letters next to each other (in a down clue, some letters hold up others).
'the motor car' becomes 'jack' (I can't explain this - if you can you should believe this answer much more).
'straw' put after 'jack' is 'JACK-STRAW'.

'and' is the link.

Can you help me to learn more?