It's becoming very hard not to feel sorry for PES leader Poul Nyrup Rasmussen:* unable to run a candidate for the Commission Presidency (which will damage the PES's chances in June), he's been reduced to impotently hinting that he has someone in mind. Meanwhile, the Greens are calling for a Red-Green coalition, with an open door for others to join, and the Liberals whinge from the sidelines that the PES isn't coherent enough or credible enough to put forward a candidate.
At the same time, there's no guarantee that the Liberals will support an anti-Barroso. Even if the PES and Greens-EFA do well enough in June, the coalition needs to be large to stand up to the EPP and the Council. Given the internal party splits in the PES (UK's Labour will do badly in the election, but with Spain and Germany, it makes up the (at least potential) core of PES in the EP), along with the strong left-right differences within the Liberals (contrast the UK's LibDems with Germany's FDP), any coalition must be big and coherent enough to withstand both its internal party splits and to wage a strong campaign against the EPP and the Council. The PES really need a plurality in the EP here, since it's unlikely that they'll be able to succeed against the Council if the Council can point to the EPP as the winners.
Of course, the EPP have some of their own problems, with the UK Conservatives breaking away from them (well, away from the EPP-aligned ED anyway), but this is unlikely to dilute centre-right support for Barroso in the EP.
I wonder if the PES might loose a few seats to the Greens, since in several countries the PES parties are either highly unpopular (UK), or have faced coherence and credibility problems (Germany and France). In Germany, the Greens tend to be the natural allies of the SPD, and their alignment in the run up to the September federal elections may further boost the credibility of the Greens among dissatisfied SPD voters who don't want to vote for the hard left. I doubt the Green's calls for EP coalition will boost their credibility much in the public's mind without an actual candidate to rally behind, but it may have a small effect. (On the other hand, a loss for the Greens has been predicted).
The PES are clinging on to the outside chance of a plurality or coalition, and have hit out against suggestions of appointing the new Commission President quickly after the new EP convenes. Nevertheless, we'll probably be left with the pitiful outcome of PES appeals for Barroso to become more socialist.
*(As ever, not to be confused with the innumerable other Rasmussens (ok, 2 others). Which makes a nice change for me, since Irish politicians with the same name are 99% likely to be related).