Like so many legislative arguments, this week’s intensified debate about the gender gap in wages has been obscured by a fight over which side has the better statistics.  

President Barack Obama and his fellow Democrats in the Senate like the Census Bureau data, which shows total earnings by women were 77 percent of what American men made in 2012. Republicans and business groups point instead to 2012 numbers from the Bureau of Labor Statistics, which suggest a narrower chasm: Women earned 86 percent of what men got.  

Which formula offers the fairest measure is ultimately beside the point on both policymaking and political grounds.  

No matter how many caveats and qualifiers are factored into the calculations, the result from those and all the other government and academic studies is consistent. Women are still paid measurably less than men for doing the same work. And the Republicans in Congress are steadfastly opposed to the legislative remedies they’ve been offered for closing the gap. Both truths have remained essentially unchanged for years.  

What has changed is the political gender gap, steadily widening and reaching record proportions — to the seemingly obvious and dangerous detriment for the Republicans. Looking only at results for the major party nominees in 2012, Obama won among women (who cast 53 percent of the vote) by a whopping 12 points but lost the male vote to Mitt Romney by 8 points — a 20-point gap that had not come close to being matched in presidential polling done by Gallup since 1952. In the past six elections (since Michael Dukakis lost the female vote as part of his landslide defeat in 1988), the Democratic nominee has won women by an average of 10 points.  

Even in the 2010 midterms, when Democrats lost control of the House by losing the national congressional vote by 7 points in the tea party wave, they managed to win 49 percent of women who showed up at the polls.  

The advantage Democrats have built and sustained with female voters is dramatically underscored by the evolving congressional roster.  

When Nancy Pelosi won her special House election in 1987, she became the 14th Democratic woman in a Congress with 12 GOP women.  

Today, Pelosi is one of 20 females in the Democratic delegation from California alone. At the same time, there are only 23 women in all of the Republican lawmaking ranks. (There are 78 Democratic women in Congress.)  

On top of these numbers are now added the particularities of this year’s midterm elections, in which the singular story is whether the GOP wins control of the Senate. And, through coincidence or fate, the path for that victory will require a collection of GOP men to vanquish some of the nation’s most prominent Democratic women. Challengers for the Republicans (all of them men) will need to knock off at least one of the three female incumbents in the most electoral danger: Mary L. Landrieu of Louisiana, Kay Hagan of North Carolina and Jeanne Shaheen of New Hampshire. Meanwhile other men of the GOP must successfully defend seats their party holds now against the most prominent Democratic Senate aspirants of the year: Alison Lundergan Grimes in Kentucky and Michelle Nunn in Georgia.  

The incontrovertible takeaway is that female voters (as well as candidates) have been and remain essential to Democratic successes at both the presidential and congressional levels. The party’s leaders are keenly aware of this. That’s why you’ve seen this week’s coordinated effort by Obama and an uncompromising Senate Democratic leadership to highlight their commitment to closing the pay gap — and to portraying the GOP as “seemingly opposing any efforts to even the playing field for working families,” as Obama said at a White House event Tuesday.  

The legislation is designed to promote gender equity in compensation by requiring that businesses who get sued for wage discrimination prove that any disparity is job-related. If they lose, they would be subjected to both compensatory and punitive damages.  

The bill would also bar employers from punishing workers who share their salary information, the most straightforward way for a woman to find out if she’s being paid less than a male colleague doing the same job.  

That was the prohibition that Obama applied to all federal contractors by executive order Tuesday. He also directed the Labor Department to start requiring those contractors to provide more data about their pay scales, including details by gender and race. (Disclosure: CQ Roll Call’s paid subscriptions cost enough that our company is classified as a federal contractor.)  

Republican leaders are amply aware of their gender gap challenges, which makes their preparations to thwart the legislation on Wednesday so remarkable.  

The four GOP women in the Senate — Kelly Ayotte of New Hampshire, Susan Collins of Maine, Deb Fischer of Nebraska and Lisa Murkowski of Alaska — have prepared an alternative they say would combat pay inequities without waves of new litigation or regulation. But once Majority Leader Harry Reid of Nevada vowed to prevent a vote on that narrowing amendment, the Republican caucus prepared to block debate from even starting .  

Similar legislation died in each of the last two election years because every GOP senator voted to sustain a filibuster. Republicans didn’t win control of the Senate in either 2010 or 2012, of course.  

Presumably they are betting the third time can still be the charm, the twin economic and political gender gaps notwithstanding.