Mamata Banerjee's Trinamool Congress is indispensible to UPA's bid to safely negotiate the looming presidential election in June as Trinamool's 47,890 electoral votes, or 4% of the electoral college, can tilt the balance in almost any political permutation. But while Congress needs its moody ally - as also regional biggies like Samajwadi Party and Bahujan Samaj Party - the threat of an opposition coup looks remote. Only desertions from UPA and a grand alliance of NDA, Left and regional parties can pose a threat.