  Ranges of differentiated abstention are shown to reverse an "exact" poll
estimate on voting day allowing the minority candidate to win the election. In
a two-candidate competition A and B with voting intentions at $I_a$,
$I_b=1-I_a$ and respective turnout at $x$ and $y$, there exists a critical
value $I_{ac}$ for which $I_{ac}<I_a<\frac{1}{2}$ yields an actual election
outcome $v_a>\frac{1}{2}$. The reversal may occur without any change of
individual choices. Accordingly, for a set of turnouts $x$ and $y$ the minimum
voting intention $I_{ac}$ required for A to win the final vote can be
calculated. The various ranges of $x$ and $y$ for which $I_{Ac}$ is smaller
than the expected 50\% barrier are determined. The calculations are applied to
the coming 2017 French presidential election for a second round scenario
involving the National Front candidate Marine Le Pen against either the Right
candidate Fran\c{c}ois Fillon or the Center candidate Emmanuel Macron. Several
realistic conditions are found to make Marine Le Pen win the election despite
voting intentions about only 40-45\%.
