The most damning polling evidence yet of what really should have been obvious from the word go - that entering into coalition with the Tories can only harm the Liberal Democrats electorally. How was a rational voter ever going to react to a True Blue Tory Budget? Those who approve will be minded to cast their vote for the 'real thing' rather than the little helpers, while those who disapprove will hardly be inclined to support either coalition party.
I sometimes wonder if their experience in coalition in Scotland led the Lib Dems into a slight false sense of security - because it's certainly true that it took far longer than anyone anticipated for them to start paying the price for propping up Labour at Holyrood. But my guess would be that can be explained by Labour being overwhelmingly perceived as "the government" by virtue of their dominance at Westminster. The Liberal Democrats were able to enjoy the best of both worlds by being able to demonstrate that a vote for them was no longer entirely wasted, while sitting back and allowing Labour to take the hit for anything that went wrong.
That's a luxury that simply won't be afforded to them this time - they could hardly be more exposed.