  We show that the well-known family of $2$-lobed Delaunay tori $\;f^b\;$ in
$\;S^3,\;$ parametrized by $\;b \in \mathbb R_{\geq1},\;$ uniquely minimizes
the Willmore energy among all immersions from tori into $3$-space of conformal
class $\;(a, b)\;$. As a corollary we obtain an alternate proof of the Willmore
conjecture in $3$-space. This new strategy can be generalized to arbitrary
codimensions provided a classification of isothermic constrained Willmore tori
is possible and all $\;f^b\;$ remain stable in all codimensions.
