Harry Reid effectively owns the U.S. Senate.

Democrats and Republicans have long debated how Reid managed to get such a tight grip on the upper chamber. But there is no debating this much: Nothing happens on the floor, or in committee, without the Nevada Democrat's approval.

Most important Senate legislation is written in Reid’s office and sent directly to the floor for a vote on final passage, sidelining committee chairmen who historically have functioned as an influential and quasi-independent force. In the past, a bill would not go to the floor before a series of votes and amendments in whatever committee, or committees, had jurisdiction over the policy it affected.

Reid has sent bills directly to the floor 74 times, according to statistics provided by the office of Senate Minority Leader Mitch McConnell, R-Ky. That's 10 times more than his predecessors during a decade-long span.

In November, Reid took the unusual step of breaking the Senate's own rules to change them, resorting to the "nuclear option" to limit the minority party's use of the filibuster. The controversial move strengthened the Democrats' power to defeat Republican procedural blockades of President Obama's executive branch and judicial appointees. The administration is now virtually guaranteed that any nominee it sends to the Senate will be confirmed.

"I wish we had not had to make this change in order to be able to confirm critical nominees for senior administration positions and judgeships," said Sen. Chris Coons of Delaware. "[But] in my three years here there was a remarkable amount of obstruction and delay through the significant overuse of the filibuster."

Even Obama has felt the force of Reid's political muscle. The president used his State of the Union address to urge Congress to grant him “fast track” authority to negotiate trade deals, which is crucial to winning the trust of trading partners. But most Senate Democrats opposed fast track, and a few days later Reid summarily announced that the chamber would not consider trade legislation this year.

But Reid, 74, remains perhaps Obama’s staunchest ally in Congress, and Democrats argue that Reid needs the power to act decisively and often unilaterally to overcome Republican obstructionism.

“He has no regrets but thinks it’s sad that it came to this,” added Adam Jentleson, Reid’s chief spokesman. “There’s really nobody on the other side of the aisle for him to work with.”

In the seven years since Reid ascended to Senate majority leader, his stewardship of the chamber has steadily evolved to resemble that of a domineering House speaker.

The House parliamentary rules are geared toward affording the majority party unchecked power. As long as the speaker musters a majority of House votes, 218 out of 435 votes, there’s little the minority party can do to influence the debate, shape legislation or block bills that it opposes. The majority’s built-in control over the chamber extends to the committees.

The Senate’s parliamentary rules were designed to forge consensus between the parties and ensure that the minority maintained a level of influence. Minor Senate business, such as a member delivering a floor speech, requires the “unanimous consent” of all 100 senators, and even the minority party’s most junior member has the power to influence the debate and shape legislation.

Most often, that power manifests itself through the use of the filibuster to block legislation or presidential nominees, or through an amendment process that enables individual senators to alter legislation after it is brought up for consideration on the floor. These parliamentary tactics have become more widely used over the past 20 years, to a degree that almost no legislation passes the Senate without getting 60 votes.

As the Senate minority leader, from 2003 to 2007, Reid was an ardent defender of the minority’s right to exercise these powers. He used them regularly, citing Senate tradition.

When the Republicans were in charge, the Nevada Democrat successfully fought to kill a GOP attempt to diminish the minority's ability to block President George W. Bush's Supreme Court nominees.

At the time, the Republicans had 55 votes, the same number as the Democrats have today, and GOP leaders threatened to invoke the nuclear option and change Senate rules with a simple majority of 51 votes, rather than the required 67, and reduce the number needed to overcome a filibuster of judicial nominees from 60 to 51.

Almost a decade later, Reid engineered a similar overhaul of parliamentary procedure. His changes affected all executive branch and lifetime judicial appointees other than Supreme Court candidates.

Reid’s maneuver came with a price, though — a hyper-partisan atmosphere in which the Republican minority is angry and even more determined to fight.

Sen. John McCain, R-Ariz., who has served with Reid for three decades, has taken to referring to the majority leader as “the dictator.”

Said a senior Republican Senate aide, with palpable frustration: “He’s basically running this place like a House leader.”

For Republicans, Reid's autocratic leadership is best defined by the number 4. From July through late January, Reid allowed only four votes on GOP-sponsored amendments to legislation. The amendment drought was broken when Reid allowed votes on three Republican amendments to a flood insurance bill. By contrast, Senate Republicans say, the majority House GOP allowed floor votes on 83 amendments sponsored by House Democrats during that same period.

Republicans say that restoring the role of committees in crafting bills, and allowing regular floor votes on GOP amendments, could immediately reduce the tension that has strangled the legislative process and poisoned personal relationships. Democrats counter that Reid still believes in protecting minority rights, but that the Republicans under McConnell are more concerned with conducting a vendetta against Obama than working collegially on legislation.

Senate Democrats say that half of all filibusters in the history of the chamber have been conducted by the Republicans since Obama took office in 2009. Additionally, of the 23 U.S. District Court nominees who have been filibustered, 20 were Obama nominees, according to statistics provided by Reid’s office.

“The Republicans have done everything to undermine the president’s agenda, so Sen. Reid and his caucus adjust accordingly and vowed not to let the Republicans get the best of them,” said Jim Manley, a former Reid aide.

Reid's aggressive leadership has had a political side benefit. Vulnerable Senate Democrats up for re-election in 2010, 2012 and now 2014 have been protected from countless tough votes on politically tailored Republican amendments that might have caused them grief with voters. Democrats are defending a six-seat majority that relies on holding a handful of seats in conservative states. Reid's strategy of preventing votes on Republican amendments, including some related to Obamacare, could prove significant in helping them preserve the majority.

Reid continues, as he has from the first day of the Obama administration, to do the heavy lifting for the president's agenda, notwithstanding his rejection of Obama's request for “fast track” trade authority. On Iran, perhaps Obama's signature diplomatic initiative, the majority leader has been the consummate team player. As a strong supporter of Israel, Reid might personally favor slapping Iran with new sanctions. But he has delayed a vote on the bill to give the administration time to convince Democrats to drop their support for the legislation.

In 2010, when the Affordable Care Act was on life support, it was Reid who saved the bill. He muscled it through the Senate using questionable parliamentary tactics, ensuring that it reached Obama’s desk. Republicans assumed control of the House in 2011, and it’s only because of the Reid-run Senate that Obama’s agenda has seen the light of day on Capitol Hill since then.

The president has vetoed only two minor bills, and that is primarily because of Reid.

On the surface, Reid may not seem like a particularly effective leader. He has a history of making inarticulate, even offensive statements for which he was later forced to apologize. Enter the terms “Harry Reid” and “gaffe” into an Internet search engine and thousands of articles are likely to pop up.

But behind the scenes, Reid is a master politician and strategist. He has few equals in using the Senate’s arcane and complicated rules to achieve his legislative ends. Among his Democratic colleagues, Reid is considered a patient listener who shuns attention in favor of promoting others. Both Democrats and Republicans who have dealt with him say Reid engenders deep loyalty by figuring out what people want and then delivering for them.

Reid, a former amateur boxer and Capitol Police officer, was once targeted for assassination by someone who did not like a decision he made as chairman of the Nevada Gaming Commission. If nothing else, his background shows that Reid doesn't shy from confrontation.

“This is like amateur hour compared to what he dealt with back in the '70s in Nevada,” a Republican lobbyist said. “He's tough as nails but very soft-spoken, so people underestimate him.”