The project, whose grand vision is to create a combined further and higher education presence on the one site, was thrown into doubt when Glasgow University threatened to pull out.
The university claims it is being shortchanged by the Scottish Funding Council, which has turned down its request to increase the number of students funded at Crichton from 88 to 300. The campus also has students from Bell College and the University of Paisley, and a new pound;28 million Dumfries and Galloway College is due to move there within two years.
The funding council argues that it cannot be expected to respond to every request for additional resources and says the university should be able to set its own priorities, which would allow it to sustain provision at Crichton "if it saw it as sufficiently strategically important to do so".
The university counters that the Crichton is now the only part of its operations running at a deficit, of pound;800,000 a year, which is "unsustainable". It envisages a phased withdrawal over three years.
Mr Salmond said a higher education research and teaching presence was vital for the southwest of Scotland, and he urged the funding council to look at all the factors. Mr Mundell described it as "beyond comprehension" if the campus was lost for the sake of pound;800,000 a year.