Montana Sen. Max Baucus will retire instead of running for reelection in 2014, meaning one of the most influential Democratic lawmakers in Congress will step down at the end of next year. Even as he's had a "D" in front of his name and can list accomplishments many Democrats liked, Baucus also had a knack for angering his party over the years.

Here's a look back at some of the most significant occasions the Montana Democrat irked fellow Democrats:

1. He voted against background checks: Baucus was one of just four Democrats who voted against a bipartisan compromise to expand background checks on gun sales last week, helping defeat an amendment for which the White House and gun control advocates lobbied heavily. The news that Baucus is retiring is sure to anger pro-gun control lawmakers even more, since unless he came to his decision in the last six days, he knew he was not bound by electoral considerations when he cast his vote. When pressed about his vote last week, Baucus gave a one word answer: Montana.

2. Tax reform: The Washington Post's Lori Montgomery recently took a close look at Baucus's tax reform effort:

Baucus is insisting on overhauling the individual tax code as well as the corporate code, a position in line with the GOP but at odds with many Democrats. The Obama administration has promoted corporate reform, but has been indifferent to far-reaching changes to the individual tax code.
Privately, senior Democrats dismiss Baucus’s activities, saying tax reform will not happen unless Obama strikes a broad deal with Republicans that includes $600 billion more in taxes over the next decade. But Republicans are unlikely to agree to higher revenue without a tax-code rewrite; aides said Camp is pressing GOP leaders to demand tax reform in exchange for supporting a higher federal debt limit.

Baucus also was one of only four Democrats to vote against the Senate budget, decrying the plan's proposed tax increases.

3. Clashes over health care: To be clear, Baucus helped write the health care reform law that President Obama signed, and played a critical role in getting the measure passed. But along the way to passage and even its aftermath, Baucus has made moves that have bothered Democrats. He shut out liberal advocates of a single-payer system from hearings in 2009, something he later said was a mistake, and he voted against a pair public option amendment proposals. He also extended negotiations for three months, giving Republican opponents more time to ramp up their opposition. And just this month, he said he saw "a huge train wreck coming down" in the implementation of the law.

4. He supported a Republican-led Medicare prescription drug benefit plan: In 2003, Baucus broke ranks with his party to support a prescription drug benefit that Republicans supported. Critics charged that the plan, known as "Medicare Part D," was good for drug manufacturers and insurance companies, but not for the Medicare program. But Baucus may be getting the last laugh on this issue; these days, it is wildly popular among seniors.

5. He joined Republicans in support of the Bush tax cuts: Baucus co-wrote the 2001 tax cut plan then-President George W. Bush eventually signed, angering other Democratic lawmakers who fought against the measure. Baucus was the first Senate Finance Committee member to break ranks with his party's opposition to the package. It's important, though, to note that Baucus also bucked Bush where he disagreed with him over the years. An example: He fought against Bush's plan to privatize social security in 2005, killing the proposal.