WASHINGTON — Ten years after a financial crisis rocked the nation’s economy, the Senate is poised to pass legislation that would roll back some of the safeguards Congress put into place to prevent a relapse.The move to alter some key aspects of the Dodd-Frank law has overwhelming Republican support and enough Democratic backing that it’s expected to gain the 60 votes necessary to clear the Senate. Several Democratic lawmakers facing tough re-election races this year have broken ranks with Minority Leader Chuck Schumer, D-N.Y. and Sen. Elizabeth Warren, D-Mass.The legislation would increase the threshold at which banks are considered too big to fail. Such banks are subject to stricter capital and planning requirements, and lawmakers are intent on providing them relief in hopes that it will boost lending and the economy.Banks have long complained about the cost of complying with the many requirements of Dodd-Frank. Under the Senate bill, some of the nation’s biggest banks would no longer have to undergo an annual stress test conducted by the Federal Reserve. The test assesses whether a bank has enough capital to survive an economic shock and continue lending. Dozens of banks would also be exempted from making plans called “living wills” that spell out how the bank will sell off assets or be liquidated in a way that won’t create chaos in the financial system.The legislation increases from $50 billion to $250 billion the threshold at which banks are considered critical to the system. The change would ease regulations on more than two dozen financial companies, including BB&T Corp., Sun Trust Banks Inc. and American Express.