President Barack Obama's Democratic Party, which now holds a 55-seat majority in the Senate, can be sure of keeping 45 of them after Election Day. Republicans will hang on to 44 of their 45 seats.
That leaves 11 close races to settle the outcome.
Democrats or independents lead in just three of them. Incumbent Sen. Kay Hagan holds a slim advantage over Thom Tillis in North Carolina. Incumbent Sen. Jeanne Shaheen leads Republican Scott Brown in New Hampshire. And business executive Greg Orman—who calls himself an independent but all Democrats are rooting for him—maintains a razor-thin advantage over Republican incumbent Pat Roberts in Kansas.
Republicans lead in eight of these battleground races. In Alaska, Arkansas Colorado and Louisiana, Republican challengers have built steady leads over respective Democratic incumbents Mark Begich, Mark Pryor, Mark Udall and Mary Landrieu. In open seat contests, Joni Ernst has moved ahead of Bruce Braley in Iowa, business executive David Perdue leads Michelle Nunn in Georgia, and ex-Gov. Mike Rounds has the advantage in South Dakota's three-way race. The sole embattled Republican incumbent—Senate Minority Leader Mitch McConnell of Kentucky—has the edge over Democratic Secretary of State Alison Lundergan Grimes.
Read MoreRepublicans unlikely to sweep midterms: NBC/WSJ Poll
If those leads hold, McConnell will lead a 52-seat Republican majority in the Senate next January.
History tells us some of those leads will NOT hold. Roberts has been making headway against Orman in Kansas, which has elected only Republican senators since FDR's time. Nunn has been moving up in Georgia, where demographic change in recent years has swelled the proportion of Democrat-friendly non-white voters.
Read MoreIn Kentucky Senate race, will verve upend sure-footed experience?
Moreover, at least some candidates trailing at the very end are likely to win anyway because their campaigns do a better job of finding and mobilizing potential voters that public pollsters overlook. That's how Democratic Sen. Michael Bennet of Colorado, currently chairman of his party's Senate campaign, won his seat four years ago.
As a result, Democrats still have a chance to maintain their majority, and with it control of the Senate agenda for the last two years of Obama's presidency. But what we can see at this point makes it clear: They will need more of those fortunate breaks to fall their way than Republicans do.