For years, as their national poll ratings have remained stubbornly low, the Lib Dems have reassured their members that their vote is holding up in those seats where they are incumbent, particularly where the Conservatives are the main opposition. The Eastleigh by-election, in which the party comfortably held off a challenge from Ukip and the Tories, was heralded as proof of this. With the Conservatives in second place in 37 of their 56 seats, the party is confident that tactical voting by left-leaning voters, combined with their MPs' local standing, will allow them to retain around 40 of their constituencies.
But Lord Ashcroft's new poll of Tory-Lib Dem marginals suggests such optimism may be misplaced. Based on current voting intentions, it found that the yellows would lose seven of their most marginal Tory-facing seats (see table below) to their coalition partners. Surprisingly to some, this is partly due to the large number of voters (13 per cent) the party has lost to Ukip. But as I've noted before, the Farageistes have replaced the Lib Dems as the natural party of protest for voters who dislike both the government and the opposition.
It's important to remember, as Ashcroft always does, that this is a snapshot, not a prediction. Around half of voters are open to changing their mind, offering the Lib Dems to chance to recover lost ground as the general election approaches. Those who have defected to Labour, for instance, may baulk at the prospect of allowing a Tory in through the back door. But at the very least, it suggests that the party should be anxious about its position in these seats.
With the Lib Dems likely to struggle in Labour-facing areas, most notably London and Scotland (the pollster Lewis Baston predicts that they could lose 10 of their 11 seats in the country), the reasons for optimism are growing ever harder to find.