  A search for flavor-changing neutral current interactions of the top quark
(t) and the Higgs boson (H) is presented. The search is based on proton-proton
collision data collected in 2016-2018 at a center-of-mass energy of 13 TeV with
the CMS detector at the LHC, and corresponding to an integrated luminosity of
138 fb$^{-1}$. Events containing a pair of leptons with the same-sign electric
charge and at least one jet are considered. The results are used to constrain
the branching fraction ($\mathcal{B}$) of the top quark decaying to a Higgs
boson and an up (u) or charm (c) quark. No significant excess above the
estimated background was found. The observed (expected) upper limits at 95%
confidence level are found to be 0.072% (0.059%) for $\mathcal{B}$(t $\to$ Hu)
and 0.043% (0.062%) for $\mathcal{B}$(t $\to$ Hc). These results are combined
with two other searches performed by the CMS Collaboration for flavor-changing
neutral current interactions of top quarks and Higgs bosons in final states
with a pair of photons or of bottom quarks. The resulting observed (expected)
upper limits at 95% confidence level are 0.019% (0.027%) for $\mathcal{B}$(t
$\to$ Hu) and 0.037% (0.035%) for $\mathcal{B}$(t $\to$ Hc). These results
constitute the most stringent limits on these branching fractions to date.
