Washington (CNN) -- With South Dakota Democrat Tim Johnson's announcement this week that he will not seek re-election this year, the recent string of Senate retirements has the political class debating whether Republicans have a real shot at taking control of the upper chamber.
But this biennial parlor game overlooks a stunning dynamic that has been developing on Capitol Hill over the past decade: massive turnover.
Think back to late 2004, when a young hotshot from Illinois had just been elected to the Senate. National TV appearances led to obvious questions about his future political plans, but the senator-elect joked that he would finish out a full term, considering he was entering the upper chamber as its 99th-ranking member.
• If Barack Obama had stayed in the Senate, he would be ranked 46th today. Given all the retirements that have been announced for the 2014 election cycle, he'd be ranked at least as high as 39th -- and maybe higher -- in early 2015. In other words, he would have taken a giant leap in seniority had he waited until 2016 to run for president.
• Only 32 current senators were in office in 2001 for the September 11 attacks. That number will shrink to 28 -- perhaps even lower -- when the next Congress convenes in early 2015.
• Since the Republicans last had the Senate majority headed into the 2006 midterm elections, 54 new senators have joined the chamber. (Fifteen new members have been sworn in since last fall's election; 14 new members joined after the 2010 election and another 15 after the 2008 election. There were 12 new senators as of the 2006 elections -- and 11 of those remain. Virginia Democrat Jim Webb served just one term and was succeeded by Democrat Tim Kaine.)
A few lions of the Senate remain, like Vermont Democrat Patrick Leahy. The Senate's most-senior member has served 38 years.
But so many of his contemporaries have left the building.
This year, West Virginia Democrat John Rockefeller, New Jersey Democrat Frank Lautenberg and Iowa Democrat Tom Harkin decided to call it quits after 30 years each. Michigan Democrat Carl Levin, who is also not seeking re-election next year, will have 36 years of Senate service to his name when his successor takes office in early 2015.
Last cycle, it was North Dakota's Kent Conrad (D), Indiana's Richard Lugar (R), New Mexico's Jeff Bingaman (D) and Wisconsin's Herb Kohl (D), among many more. In recent years, the Senate has lost Edward Kennedy, Robert Byrd, Daniel Inouye and Craig Thomas to death in office. Other long-time senators like Joe Biden and John Kerry have moved to the executive branch.
Consequently, a much different Senate is emerging.
The first Japanese-American woman, Mazie Hirono, and the first openly gay woman, Tammy Baldwin, joined the Senate this year. The country's most exclusive club boasts a record number of women, 20; a Cuban-American Republican and an African-American Republican both in their 40s; and a growing number of senators with young children (and who still are many years away from grandchildren).
Another case in point: If a Democrat succeeds Lautenberg in deep-blue New Jersey, it could be Newark Mayor Cory Booker, who is running for the open seat. Lautenberg at 89 years old is more than twice the age of Booker, who is 43.
And on the other side of the aisle, aggressive conservatives are shaking things up, too. Already running for Johnson's seat in South Dakota is 58-year-old Republican Gov. Mike Rounds. But the Senate Conservatives Fund blasted Rounds on Tuesday for not being conservative enough.
Republican campaign sources say the group has met with Republican Rep. Kristi Noem to recruit her into the race instead. Noem, a 41-year-old mother of three, is quietly considering the race. Of course, Democrats have their own younger options, like former Rep. Stephanie Herseth Sandlin, 42; or Johnson's son, U.S. attorney Brendan Johnson, 38.
Even though party leaders on both sides of the aisle like to keep retirements each cycle to a minimum, Democratic operatives say they're not disappointed in the predicament this year, because those with access to early polling data in states like West Virginia and South Dakota say some of the younger, newer faces in those states are polling better against potential Republican opponents than the veteran senators did.
Senate Historian Donald Ritchie says that overall, the trend is a cyclical one, but he acknowledges that the current dynamic stands out.
"We have 45 senators serving in their first six-year term," he said. "It's quite remarkable. It's the largest turnover we've had since the late 1970s."
Ritchie remembers a long list of retirements in 1976 and 1978, followed by a rout of veteran senators in 1980.
"This is a very personality-driven institution," he said. "When you change some of these larger-than-life personalities, it really changes the place."
Ritchie expects that some of the newer members will become veteran, seasoned members in time for a new generation, but he conceded that the brain drain in the upper chamber does infringe on some of the important expertise.
Indeed, according to a handful of experienced Washingtonians who have worked in and around the Senate, the heavy turnover cuts both ways.
Leadership aides close to Senate Minority Leader Mitch McConnell say that he and some of his staff believe there's more energy in the upper chamber now and more of a willingness to fight for causes. Despite some of the nostalgia surrounding some of the old bulls who were more comfortable compromising and cutting deals, they believe the GOP conference is working harder than ever.
Democratic Senate aides say a positive outcome of the Senate's changing face is that Americans may now find them more relatable. And it makes the tough task of recruiting new candidates easier with a diverse caucus because more potential recruits can actually see themselves in the Senate.
Bob Stevenson, a Republican, and Jim Manley, a Democrat, were longtime and highly influential staffers within the Senate leadership.
Both harbor typical complaints about the opposing party, but they both long for the days of compromise, when some of the younger, newer members respected their elders.
"Making the Senate work requires cooperation and compromise," Stevenson said. "Deal-making and compromise have never been 'easy,' but the leaders forced it on the rank-and-file. Not as much today."
Stevenson, who advised former Republican majority leader Bill Frist, continued, "Sharp division in the country and 'compromise equals weakness' is reflected in the younger members. Great political strategy but not conducive to governing."
Manley advised the first Democratic majority leader after Frist, Harry Reid.
Now outside the Senate, he complained about some of the same things: that the massive turnover also means a loss of institutional knowledge.
"There's no one to negotiate with in the House with a Republican caucus full of tea party types," he said. "After 21 years in the Senate, I've come reluctantly to the conclusion that the process on Capitol Hill is broken."
Manley continued, "Times have changed, and the Senate's changed. It's the influx of new members from the House that brought all the bad habits they developed in the House."
And citing Texas Republican Ted Cruz, he said, "This is a potent group of freshmen who have no respect for the Senate as an institution, who would rather burn the place down so they can remake it again."