By DANA LIEBELSON

Thomas MacKenzie, the former Northrop Grumman lobbyist who was awarded a large severance and bonus prior to taking a job on Capitol Hill in 2011, also owned between $100,000 and $250,000 in Northrop stock during that time, according to his ethics disclosure statement.

"It's not uncommon for a senior K Street lobbyist to have a quarter of a million dollars tucked away in stock. But it is uncommon for someone who is a congressional staffer," Craig Holman, government affairs lobbyist at Public Citizen, told the Project On Government Oversight. "This poses a very serious conflict of interest."

The disclosure statement, which was filed in August 2011, covers the period between Jan. 1, 2010 and June 15, 2011. MacKenzie joined the House Armed Services Committee in March 2011, and earned about $108,000 in that year.

This is MacKenzie's second trip through the revolving door. Before working for Northrop Grumman, he was a staffer on the Senate Armed Services Committee from 2000 to 2005, according to Legistorm.

It's unknown whether MacKenzie still owns Northrop stock, as this information isn't readily available to the public. However, under the Stop Trading On Congressional Knowledge (STOCK) Act which passed earlier this year, senior staffers must file reports on personal transactions valued over $1,000 within 45 days (with some exceptions) -- beginning July 3.

The STOCK Act applies to congressional staffers who make a monthly salary of at least $9,962 for any two months during a calendar year. According to Legistorm, MacKenzie's salary seems to qualify for the first quarter of 2012. So once the STOCK Act kicks in, it appears he should be subject to this disclosure requirement.

However next year, this qualifying salary could be irrelevant to MacKenzie and others, according to POGO Director of Public Policy Angela Canterbury.

"There is a sneaky way around the reporting -- which is that lump sum bonuses don't trigger the reporting requirement," Canterbury said.

According to the guidance from the House Ethics Committee:

Paying a bonus through a lump sum payment rather than through raising an employee's base rate of pay does not trigger the Ethics in Government Act filing requirements and therefore would not trigger the requirement to file Periodic Transaction Reports.

Canterbury added, "We will be watching to ensure this gigantic loophole isn't exploited by some in Congress to avoid reporting."

However, MacKenzie and others are barred from using any information gleaned while working on the Hill on personal stock transactions, as part of the new explicit insider trading ban.

But even under the STOCK Act, there are no restrictions that apply to a former lobbyist like MacKenzie owning a large amount of stock in his old company. And the appearance of a conflict of interest, particularly in this case, where MacKenzie will most likely be working on the defense issues he used to lobby -- erodes the public trust.

"Large defense contractors like Northrop should not be allowed to capture the House Armed Services Committee with their lobbyists," Canterbury said. "This revolving door only keeps the gravy train of taxpayer dollars flowing to these for-profit players -- even if it is not in the interests of our national defense and economy."

Dana Liebelson is POGO's Beth Daley Impact fellow.