  We investigate the origin of the large clustering signal detected in the
angular distribution of the radio sources in the TGSS catalog. To do so, we
cross-correlate the angular position of the radio sources with the Cosmic
Microwave Background (CMB) lensing maps from the Planck satellite, since
cross-correlation is expected to be insensitive to source of possible
systematic errors that may generate a spurious clustering signal. The amplitude
of the angular cross-correlation spectrum of TGSS-CMB lensing turns out to be
much smaller than that of the TGSS auto-spectrum and consistent with that of
the NVSS-CMB lensing cross spectrum. A result that confirms the spurious origin
of the TGSS large scale clustering signal. We further compare the two
cross-spectra with theoretical predictions that use various prescriptions from
the literature, for the redshift counts of the radio sources, $N(z)$, and their
bias $b(z)$. These models, that assume a $\Lambda$CDM cosmology and that were
proposed to fit the NVSS auto-spectrum, fail to match the cross-spectra on
large scale, though not by far. When the bias relation is let free to vary
(model predictions are rather insensitive to the choice of the N(z)) the
quality of the fit improves but a large bias ($ b_g = 2.53 \pm 0.11$) is
required, which does not seem to be consistent with the observed clustering
amplitude of the radio sources in the local universe. Whether this large
cross-correlation amplitude represents a problem for the radio sources models,
or for the $\Lambda$CDM framework itself, can only be clarified using next
generation datasets featuring large number of objects. What our analysis does
show is the possibility to remove the $N(z)$ and $b(z)$ degeneracy by combining
angular and cross-correlation analyses.
