For example, in Portugal, we have had as most proeminent presidents the two most active former prime-ministers. When they do arrive to presidency, they take a much more relaxed attitude. Too much relaxed.
Why is that? I do not know for certain, but I bet on the posture they have to assume as presidential candidates - which is basically a two party system. A presidential campaign is, among other things, a training camp for the candidates to "let go" their personal beliefs.
French presidential campaigns are something else.
Portuguese presidents do have some real powers, rarely used. Namely the power to throw down government and simultaneously order general elections. This has happened once - considering only the period after the 1974 revolution -, 3 years ago. They cannot veto laws, only demand a confirmation from parliament, or question proposed law's compatibility to the constitution, which will be decided by a council of judges (Constitutional Court).
Id est, to behave as a political figure, instead of someone above (or post-) politics.
