2025ApJ...991..111S

T Corona Borealis (T CrB) is a recurrent nova and a symbiotic star that is commonly highlighted as the best case for being a progenitor of a Type Ia supernova (SN Ia) within the framework of single-degenerate models. This exemplar can be tested by measuring whether the white dwarf (WD) mass (M_WD) is increasing over each eruption cycle. This is a balance between the mass ejected during each nova event (M_ejecta) and the mass accreted onto the WD between the nova events (M_accreted). I have used all 206 radial velocities from 1946 to 2024 to measure the orbital period just after the 1946 eruption, which is P_post = 227.6043 days, while the steady orbital period change ($\dot{P}$) is (-3.1 ± 1.6) × 10^–6. I have used my full 213,730 magnitude B and V light curve from 1842 to 2025 to measure the times of maximum brightness in the ellipsoidal modulations to construct the O - C from 1866 to 1946. I fit the broken parabola shape to find the orbital period immediately before the 1946 eruption, which is ${P}_{{\rm{pre}}}$ = 227.4586 days. The orbital period changed by ΔP = +0.146 ± 0.019 days. With Kepler's Law, conservation of angular momentum, and the well-measured binary properties, the ejecta mass in 1946 is 0.00074 ± 0.00009 M_⊙. M_accreted is reliably measured to be 1.38 × 10^–6M_⊙ from the accretion luminosity. M_ejecta is larger than M_accreted by 540×, so M_WD is decreasing every eruption cycle. T CrB can never become an SN Ia.