Gov. Jerry Brown’s bold $17 billion plan to build two gigantic 35-mile, 40-foot-wide tunnels under the Sacramento-San Joaquin Delta to make it easier to move water from Northern California to Southern California and to stabilize the state’s water distribution system always seemed like a tough sell. Critics were far more energized than supporters. Then last month, a huge new obstacle emerged. That’s when the Central Valley’s Westlands Water District — the nation’s biggest irrigation district — came out against the project. It had been expected to pay nearly a quarter of the $17 billion cost.