It's rare that you can get Reps. Jim Sensenbrenner (R-Wis.) and John Conyers (D-Mich.) to agree on much of anything. The former, after all, introduced the USA PATRIOT Act to the House, and sponsored H.R. 4437, the House-passed bill that would have made "illegal presence" of immigrants a felony, and which prompted huge protests by immigration activists across the country. Conyers, by contrast, is a liberal stalwart who has championed Medicare-for-all and a public jobs program for the unemployed.

But the two, along with Sen. Patrick Leahy (D-Vt.), are introducing legislation they co-wrote to strengthen the Voting Rights Act. The act's "pre-clearance" process was substantially weakened by a Supreme Court case this last spring. The new bill doesn't roll back all of that ruling, but it does expand pre-clearance and add other protections currently lacking in the act. Here's what you need to know.

The bill is a response to the Supreme Court's ruling in Shelby v. Holder, a case last spring in which a 5-4 majority struck down section 4 of the Voting Rights Act (VRA), the landmark 1965 bill securing access to the ballot box in regions with histories of black voter suppression. That was a major blow to the law, but to understand why you have to understand how section 4 fit into the VRA's overall approach.

The VRA contains two sections that enable challenges to state and local voting laws and practices:

• Section 2 enables civil suits against states, counties, and municipalities that engage in voting practices that violate the VRA. Those suits are typically filed by the Justice Department, but could also be led by private citizens affected by the alleged violations. It was unaffected by the Court's ruling.

• Section 5 requires that certain states or localities get "pre-clearance" from the Justice Department before adopting any changes to their voting laws.

Which states and localities are subject to the Section 5 process is determined by two further provisions of the law:

• Section 3 requires preclearance in cases where judges find, or jurisdictions admit to, constitutional violations in the voting process. For example, Arkansas was bailed in when a U.S. district court found that Arkansas's voting laws intentionally and unconstitutionally discriminated against African-Americans. The court invoked Section 3, requiring Arkansas to preclear changes to voting laws going forward. Travis Crum wrote an excellent law note in the Yale Law Journal in 2010 explaining how Section 3 works, if you want more information.

• Section 4 relies on historical tests — like "did this jurisdiction require a literacy test to vote in 1964?" — to determine if jurisdictions need preclearance. Most of the former Confederacy, for instance, was included because of Section 4. Now that Section 4 has been struck down, those states are free and clear.

Here's a map of the Section 4 states, which The Post graphics team created when the ruling came down: http://www.washingtonpost.com/blogs/wonkblog/wp/2014/01/16/the-supreme-court-gutted-the-voting-rights-act-now-a-bipartisan-gang-wants-to-put-it-back-together/?wpisrc=nl_wnkpm

So now, the Justice Department and private citizens can either (a) challenge voting laws in court directly with Section 2 and/or (b) use Section 3 to require pre-clearance of states with VRA violations. But preclearance has been pared back significantly.

Ari Berman at The Nation has the best rundown of what the new plan proposes. It has five basic elements:

1. It directly responds to the Supreme Court ruling by creating a new Section 4 formula for determining which places need pre-clearance. While the historical basis of the original Section 4 formula was enough to get the Court to strike it down, Sensenbrenner-Conyers-Leahy would use more recent information. If a state has five or more violations in the past fifteen years (for local areas, three violations or one violation and persistently low minority turnout), it becomes subject to preclearance under Section 5. That means Georgia, Louisiana, Mississippi and Texas would need to pre-clear changes to voting laws, but Alabama, Arizona, Florida, North Carolina, South Carolina, and Virginia — all subject to pre-clearance before Shelby — would be exempt. Further, voter ID laws cannot be included as violations for these purposes, even if they're blocked by courts or the Justice Department on VRA grounds.

2. Section 3 is strengthened significantly. Now, plaintiffs have to show that jurisdictions they want to "bail in" are engaged in intentional voting discrimination, which is tough to prove. Under Sensenbrenner-Conyers-Leahy, any violation of the VRA or another federal voting rights law (exempting voter ID laws) would be enough to trigger a section 3 bail-in, whether or not it can be proven to be intentional.

3. All 50 states and their localities are required to give notice in local media and on the Internet of any actions related to redistricting, changes in election procedures close to an election, and the movement of polling places.

4. The burden of proof required for Section 2 plaintiffs to get a preliminary injunction against a law that might violate the VRA is lowered.

5. The attorney general's ability to send observers to Section 4 states/jurisdictions is expanded to include authority to send observers to areas that have discriminated against linguistic minorities in the past.

As Berman notes, this bill would hardly roll back Shelby completely. The number of states subject to pre-clearance requirements under the bill would be significantly lower than the number this time last year, and not counting voter ID restrictions as "violations" could become a major loophole. Still, significant, bipartisan bills with a good chance of passage are extremely rare these days, and it's a big deal that Sensenbrenner — who helped shepherd the 2006 renewal of the Voting Rights Act through Congress — is lending his heft to the effort.

If you're interested in more transformative ways to ensure that voters are represented regardless of their race, ethnicity, or language, see this post from last spring, where I explained why some experts think the whole Voting Rights Act model might need to be rethought. For more on the current state of voting rights, see John Sides.