Before yielding gavel, GOP's Issa readies a final shot at 'Obamacare,' and ...

FILE - In this Sept. 30, 2014 file photo, House Oversight Committee Chairman Rep. Darrell Issa, R-Calif. listens during a hearing on Capitol Hill in Washington. One of the Obama administration's harshest congressional critics will get a final high-profile shot Tuesday when the committee grills witnesses about the president's health care law and a former adviser's comments that 'the stupidity of the America voter' helped Democrats pass the complex legislation. (AP Photo/J. Scott Applewhite, File)news3blog.blogspot.com

FILE - In this Feb. 8, 2011 file photo, Jonathan Gruber poses in his home in Lexington, Mass. One of the Obama administration's harshest congressional critics will get a final high-profile shot Tuesday when the committee grills witnesses about the president's health care law and a former adviser's comments that 'the stupidity of the America voter' helped Democrats pass the complex legislation. (AP Photo/Charles Krupa, File)news3blog.blogspot.com

One of the Obama administration's harshest congressional critics will get a final high-profile shot when the House Oversight Committee grills witnesses about the president's health care overhaul and a former adviser's remark about voters' 'stupidity.'

For four years, Rep. Darrell Issa, R-Calif., has used the committee chairmanship to probe and attack the administration on issues such as the IRS scandal, misplaced guns and U.S. deaths in Benghazi, Libya. Talk radio conservatives love him. But even some GOP colleagues say he overdoes the combative partisanship at times.

Issa, who surrenders the chairmanship next year due to term limits, will lead the questioning of former health adviser Jonathan Gruber. Gruber, an MIT economist, recently apologized for saying Americans' 'stupidity' was vital to passing the health law in 2010.

The committee also will question a top administration official who wants to be queried separately from Gruber.

The hearing comes as prominent Democrats debate the wisdom of devoting much of 2009 - Barack Obama's first year as president - to the bruising battle for the health care legislation, which finally passed without a single Republican vote. Sen. Chuck Schumer of New York is among those Democrats now criticizing the timing. Top liberals are defending Obama, creating new divisions among Democrats right after major losses in this year's elections.

Like many congressional hearings, Tuesday's session may provide partisan fireworks while doing little or nothing to change government policy. The president says he will veto any effort to overturn what Republicans call 'Obamacare,' should such a bill reach his desk after Republicans add Senate control to their House majority next year.

Gruber has made controversial and sometimes conflicting remarks during his years as a health policy adviser to then-Gov. Mitt Romney of Massachusetts, and later to the Obama administration. Some Republicans call him an 'architect' of the health care law, but others say that overstates his role. The government paid Gruber about $400,000 for his work, and he often attended White House strategy sessions on the legislation.

Videos from 2013 show Gruber telling groups that the 'stupidity of the American voter' and a 'lack of transparency' were important to passing the legislation. Gruber recently said he 'spoke inappropriately, and I regret having made those comments.'

Also testifying Tuesday will be Marilyn Tavenner, administrator of the Centers for Medicare and Medicaid Services. In an effort to distance Tavenner from Gruber's remarks, the administration asked Issa to put her on a different witness panel. Issa's staff said it was weighing the request.

Issa calls the health care law 'the poster child for this administration's broken transparency promises.'

Issa's bare-knuckled inquiries into administration policies and missteps have often infuriated Democrats while providing welcome fodder for conservative talk shows, speeches and campaigns.

His broadsides against the IRS, State Department and other agencies may have helped excite the Republican base in the November midterm elections. But Issa sometimes embarrasses GOP leaders, as when he cut off the committee microphone at an IRS hearing when the top Democrat, Rep. Elijah Cummings of Maryland, was trying to speak. And some Republican lawmakers chastised Issa when he called then-Obama spokesman Jay Carney a 'paid liar.'

Issa has clashed with the administration on numerous topics. When he accused it of improper campaigning, he tried to bring two former Cabinet members - former Health Secretary Kathleen Sebelius and former Labor Secretary Hilda Solis - before his committee. They declined.