  The recent precise experimental determination of the monopole transition form
factor from the ground state of $^4$He to its $0^+_2$ resonance via electron
scattering has reinvigorated discussions about the nature of this first excited
state of the $\alpha$ particle. The $0^+_2$ state has been traditionally
interpreted in the literature as the isoscalar monopole resonance (breathing
mode) or, alternatively, as a particle-hole shell-model excitation. To better
understand the nature of this state, which lies only $\sim$ 410 keV above the
proton emission threshold, we employ the coupled-channel representation of the
no-core Gamow shell model. By considering the $[^3$H$ + p]$, $[^3$He$ + n]$,
and $[^2$H+$^2$H] reaction channels, we explain the excitation energy and
monopole form-factor of the $0^+_2$ state. We argue that the continuum coupling
strongly impacts the nature of this state, which carries characteristics of the
proton decay threshold.
