  Using a two-band double-exchange model with Jahn-Teller lattice distortions
and super-exchange interactions, supplemented by quenched disorder, at electron
density $n=0.65$, we explicitly demonstrate the coexistence of the $n$ =
1/2-type ($\pi, \pi$) charge-ordered and the ferromagnetic nanoclusters above
the ferromagnetic transition temperature $T_{\rm c}$ in colossal
magnetoresistive (CMR) manganites. The resistivity increases due to the
enhancement of the volume fraction of the charge-ordered and the ferromagnetic
nanoclusters with decreasing the temperature down to $T_{\rm c}$. The
ferromagnetic nanoclusters start to grow and merge, and the volume fraction of
the charge-ordered nanoclusters decreases below $T_{\rm c}$, leading to the
sharp drop in the resistivity. By applying a small external magnetic field $h$,
we show that the resistivity above $T_{\rm c}$ increases, as compared with the
case when $h=0$, a fact which further confirms the coexistence of the
charge-ordered and the ferromagnetic nanoclusters. In addition, we show that
the volume fraction of the charge-ordered nanoclusters decreases with
increasing the bandwidth and consequently the resistivity hump diminishes for
large bandwidth manganites, in good qualitative agreement with experiments. The
obtained insights from our calculations provide a complete pathway to
understand the phase competition in CMR manganites.
