  We study the asymptotic behaviour of the martingale ($\psi$ n (o)) n$\in$N
associated with the Vertex Reinforced Jump Process (VRJP). We show that it is
bounded in L p for every p > 1 on trees and uniformly integrable on Z d in all
the transient phase of the VRJP. Moreover, when the VRJP is recurrent on trees,
we have good estimates on the moments of $\psi$ n (o) and we can compute the
exact decreasing rate $\tau$ such that n --1 ln($\psi$ n (o)) $\sim$ --$\tau$
almost surely where $\tau$ is related to standard quantities for branching
random walks. Besides, on trees, at the critical point, we show that n --1/3
ln($\psi$ n (o)) $\sim$ --$\rho$ c almost surely where $\rho$ c can be computed
explicitely. Furthermore, at the critical point, we prove that the discrete
process associated with the VRJP is a mixture of positive recurrent Markov
chains. Our proofs use properties of the $\beta$-potential associated with the
VRJP and techniques coming from the domain of branching random walks.
