Senate Republicans on Tuesday blocked legislation to freeze interest rates on need-based student loans, creating an election-year fight that could double loan costs for some college students. The motion to end debate secured only 52 votes, failing to meet the 60-vote threshold needed to move the bill to a final vote. Republicans and Democrats agree the student-loan rate should be held at 3.4 percent for another year, but they can’t come to consensus on how to cover the $6 billion cost. Interest rates on federal student loans will double on July 1 if lawmakers do not reach agreement. Democrats have floated the idea of a rate-freeze funded by taxpayers—in other words, with no offset. But that is unlikely to pass muster among Republicans. The House has passed a student-loan bill last month that would tap a health-care prevention fund to pay for the interest-rate freeze. The Republican-suggested offset drew a veto threat from the White House and raucous objections from Democrats. Democratic Senate leaders proposed raising taxes on so-called S-Corporation businesses to raise the money for the rate freeze. Republicans accused Democrats of attacking small businesses.