WASHINGTON — Hemmed in by solid Republican opposition, the Senate seems ready to hand a fresh defeat to President Barack Obama by blocking an election-year bill increasing the federal minimum wage.

Democrats, aware that the measure faces all but certain rejection today in the chamber they control, plan to use the vote to buttress their campaign theme that the GOP is unwilling to protect financially struggling families.

“Americans understand fairness, and they know it's unfair for minimum-wage workers to put in a full day's work, a full month's work, a full year's work, and still live in poverty,” the measure's sponsor, Sen. Tom Harkin, D-Iowa, said Tuesday.

Harkin's bill, an Obama priority, would gradually raise the $7.25 hourly minimum to $10.10 over 30 months and then provide automatic annual increases to account for inflation. Democrats argue that if fully phased in by 2016, it would push a family of three above the federal poverty line — a level such earners have not surpassed since 1979.

They also say the minimum wage's buying power has fallen. It reached its peak value in 1968, when it was $1.60 hourly but was worth $10.86 in today's dollars.

Republicans say the Democratic proposal would be too expensive for employers and cost jobs. As ammunition, they cite a February study by the nonpartisan Congressional Budget Office that estimated the increase to $10.10 could cost about 500,000 jobs — but also envisioned higher income for 16.5 million low-earning people.

Citing those job loss figures, Senate Minority Leader Mitch McConnell, R-Ky., said Tuesday, “When it comes to so many of their proposals, Washington Democrats appear to prioritize the desires of the far left over the needs of the middle class.”

Democrats needed 60 votes today to begin Senate debate. To prevail, they would need support from at least six Republicans, which seemed beyond reach.

“I can't give you a number, but I'm confident” Democrats won't succeed, Sen. John Cornyn, R-Texas, his party's vote-counter, said after GOP senators met Tuesday.

Sen. Susan Collins of Maine, one of the few Republicans considered potentially willing to let debate begin, said Tuesday she expected to oppose the legislation, saying it would hurt companies. Sen. Bob Corker of Tennessee was the only Republican to publicly state he probably would vote to allow the bill to be considered.

Sen. Mark Pryor, D-Ark., who faces a tough re-election and has said the $10.10 increase is excessive, will miss today's vote. He will be in Arkansas due to deadly storms there, an aide said.