The Conservatives are accusing Ed Miliband of preparing to "stab the United Kingdom in the back", trading away Britain's nuclear deterrent in order to secure power in a backroom deal with the Scottish Nationalists.
The campaign got nasty today: defence was the theme, but offence was taken. The Tories said Labour would abandon the Trident nuclear deterrent, to cut a deal with the SNP. Ed Miliband would be "stabbing the nation in the back" the Defence Secretary said, just as he'd stabbed his own brother in the back. But Mr Miliband deployed calm fury saying Michael Fallon had "demeaned himself and his office." It was lies and a deceit, said Labour, dragging the campaign "into the gutter".
The main political parties are wrangling over whether the UK should spend billions renewing its nuclear deterrent.
If a difference of opinion on defence didn't get in the way of the current coalition - why would it be different for Labour and the SNP?