David Cameron may have managed to equal Nick Clegg in the second debate, but pictures of the two juxtaposed together in national newspapers still present an insurmountable problem: the perception that voting Lib Dem is no long a wasted vote. And we know where that path leads.

It's in the interests of Lib Dems to play up their position in the polls - after all they've never been taken more seriously. That means fewer people who think that voting Lib Dem is a "wasted vote". But Clegg still faces two challenges that will reduce his party's vote on polling day. And he must take action to deal with them now.

The youth vote and GOTV

A large proportion of the swing to Nick Clegg comes from the youth vote (see Sami Kent today). They're less likely to be tribal about specific parties, are more desperate to see real change (of the electoral kind) at Westminster, and were largely absent from the election earlier. Some are likely to be still angry about the Iraq war. But the youth vote is notoriously unpredictable. This is the demographic least likely to vote because broadly they're just either too lazy or apathetic.

Barack Obama faced the same problem, and plenty of pollsters speculated then that Obama's poll ratings could be over-stated for this reason. Hence, much of his field operation after winning the primaries was about identifying (and to a lesser extent persuading) Democratic voters and getting them to turn out on election day.

Clegg doesn't have the same resources, clearly, but his operation might want to think less about canvassing now and more about getting out the vote (GOTV) on election day. Reaching out to university students would be a good start. Identifying Lib Dem pockets of voters and organising activists to start knocking on doors on polling day to get them out would be another strategy Cowley Street is or should be thinking about.

A Lib Dem victory almost disproportionately depends on turnout. While this applies for the others too - the Tories benefit from having voters who are energised to come out and throw out Gordon Brown. Clegg cannot assume that anger and apathy among the youth vote will automatically translate to votes on election day and needs to take action on that front (if he isn't already).

The fear factor

About 5 - 10% of voters will be voting for the Lib Dems for the first time, with the view that their vote will not be wasted. But will they take the plunge without hesitation? This paper, which looked at polls in the US, UK and Australia says that while opinion often changes during an election - on election say itself it often reverts back to near where it started.

It won't happen in this case of course - the swing towards the Lib Dems has been the biggest ever, in the shortest time ever, in recent British political history. But there will be a percentage of voters - I'd say between 2%-4% - who will bottle it at the polling booth. This is mostly why the Tories are playing up the "nightmare scenario" of the British economy nosediving in case of a hung parliament: they want people to be scared despite accusing their opponents of the same.

The author writes:

One explanation, we suggest, is that people become more responsible when stepping into the poll booth: when voting they reflect back on the government's whole time in office, rather than just responding (as when talking to pollsters) to the noise of the past few days' campaigning.

So this may help Labour more than the Conservatives.

Anger at the political class could carry on until election day and force voters out of their shell. Nevertheless, the Lib Dems cannot rest easy. But they can't play down their poll ratings either, or people voting for them tactically may switch back to their original choice. It's useful for the party, however, that most people pay little attention to the Westminster press. Once the narrative is set that they are the third party and a real player, it will take a lot to change that back. And I don't see that happening.