U.S. Reps. Stephen Lynch and Ed Markey, the Democratic rivals in the race for the U.S. Senate, have mostly voted along similar lines in the 12 years they've served together.
But there have been some significant votes on which they've found themselves on opposing sides. Here's a look at several of them.
Arming Pilots Post-9/11
Lynch won the Democratic primary on Sept. 11, 2001. The following month, he easily defeated his Republican opponent. When Lynch arrived in Washington, D.C., he found his office closed because of an anthrax scare. Many of his first votes had to do with 9/11.
One of the first big ones on which Lynch differed with Markey came the next year. It was to allow airline pilots to carry guns in cockpits. It created a two-year program to train pilots who wanted to learn how to use guns on planes.
Markey was against it.
"I thought that it would make it even more likely that there could be a catastrophic event up in the air," Markey said in a phone interview with WBUR. "And that proposal was in fact opposed by the airline flight attendants, by the TSA, and I think that they were right."
Lynch wanted to arm the pilots.
"The bill also provided self-defense training for flight attendants as well," Lynch said in a phone interview with WBUR. "We also had another parallel program that put armed air marshals on planes, but we could not cover all flights, so whereas the air marshal program cost $3,000 per flight, the training program for pilots and allowing them to have a weapon in the cockpit cost $15 per flight."
The program passed, and today thousands of pilots carry guns in the cockpit. But Markey still thinks it's a bad idea.
"I believe there could be accidental weapon discharge and pilot mishandling of the weapons, which are also risks, and again those risks are exacerbated by the tight confines of an airplane," Markey said.
In 2002, the two congressmen also found themselves on opposing sides of the issue that has most divided them over the years: abortion. Markey voted against a ban on so-called "partial-birth abortions."
"A woman should have the right to consult with her family, with her physician, with her own conscience," Markey said. "It's a decision which is very personal."
"The 'partial-birth-abortion' ban was a position taken by the American Medical Association," Lynch said. And he supported it.
"There was an amendment for cases where there was a late-term abortion where there was rape, incest or where the health of the mother was at risk, and I did support that amendment," Lynch said.
The next year, the ban became law.
In 2004, so did a measure to establish an embryo or a fetus as a legal person. Markey voted no. Lynch voted yes.
For several years running — from 2002 to 2006 — Lynch was the only member of the Massachusetts delegation to vote against allowing women in the military to use private funds to pay for abortions at overseas military hospitals.
"There is no free choice being exercised on military bases, by women or by men. It is a command society, it's basically by rank," he said in explaining his vote. "If you think about it, if a woman has an unwanted pregnancy on a military base there's a high likelihood that there was another enlisted or officer involved. What I did support was allowing women to have automatic leave, medical leave, to leave the base and to make a decision on their own."
Except in the case of rape, incest and when their own lives are in danger, women are still not allowed to have abortions on military bases.
Then, in 2009, as the House worked on the Affordable Care Act, Lynch voted to deny abortion coverage to women who receive federally subsidized health insurance. Markey voted the keep the abortion coverage.
"I did not believe there should be restrictions placed upon a woman's right to have insurance under the Affordable Care Act," Markey said.
The measure passed the House, but the Senate defeated a similar one, and so it died.
The following year, Lynch took his most famous lone stand. He became the only Massachusetts member of Congress to vote against final passage of the Affordable Care Act itself, even though President Obama spoke with him for 40 minutes to try to change his mind. Lynch had supported an earlier House version.
"It provided for a public option and avoided any taxes on health care," Lynch said. "That bill was precluded because of Scott Brown's election. It was kept from conference. Instead, we had to support a bill that took away the public option that we had put in in the House, where states could have operated a low-cost, public-option health care plan to create competition in the insurance market."
Lynch also objected to the fact that the final version taxes health care plans.
In 2011, another issue revealed the two candidates' differences. Markey and Lynch disagreed over whether to fund a defense contract that would have built F-35 fighter jet engines at the GE plant in Lynn, creating jobs in Massachusetts. Pratt & Whitney, based in Connecticut, was already making engines for the F-35. Markey voted for the GE engines.
"With a single supplier of an engine, that single supplier can charge the Defense Department whatever they want, increasing costs to taxpayers, and in tight economic times that makes no sense," Markey said. "As with any other business, multiple suppliers means competition, which drive down costs."
Lynch voted against funding the GE engines.
"The president and the secretary of defense came forward to say this is a program that we do not want," Lynch said. "There was already one engine for the F-35 and this was an alternative engine. They said we already have the other engine in service."
The House agreed with Lynch and killed the GE engine. That was the last time Markey and Lynch took opposing sides on a major vote.
This program aired on March 27, 2013.