WASHINGTON — With President Obama securing the votes Wednesday needed to assure the Iran nuclear accord will survive congressional challenge, Republicans are considering legislative options to counter the deal, including the possible reimposition of sanctions the agreement is supposed to lift.

“While the president may be able to sustain a veto with the tepid, restricted and partisan support of one-third of one house of Congress over Americans’ bipartisan opposition,” said Senator Mitch McConnell, Republican of Kentucky and the majority leader, “it will require a bipartisan Congress to strengthen our defenses in the Persian Gulf and to stand up to the inevitable Iranian violations of the agreement that will need to be addressed after he has left office.”

Republicans have been thinking through alternatives for months, knowing that Mr. Obama would probably be able to fend off efforts to override his veto of a resolution scuttling the accord. The agreement’s implementation seemed assured Wednesday when Senator Barbara A. Mikulski, Democrat of Maryland, came out in support, the 34th Democrat to do so, providing Mr. Obama with enough votes to prevent an override of a resolution of disapproval of the deal.

For its part, the House will also consider the disapproval resolution next week when Congress returns. Democrats hope to assemble enough votes to sustain a veto in that chamber, as well. A veto override must pass both the House and Senate by a two-thirds vote.