OPIOID SERIES:

Dems’ likely Senate gains

When the dust settles this November, chances are Democrats will be in charge. Not only is Barack ObamaBarack Hussein Obama Stormy Daniels’s 'View' is incorrect Trump attorneys defend Obama’s Atlantic Ocean protections Don’t let Washington’s toxic partisanship infect foreign policy, too MORE likely to be the next president, but the Democratic House advantage — currently 36 seats — is seemingly certain to grow to a margin of at least 50.

But the success or failure of the Democratic majority’s agenda will ultimately be determined in the Senate, where Republicans are struggling to retain enough seats to block the Democratic mandate via filibuster.

Democrats currently hold 49 Senate seats, and enjoy the solid support of Vermont Independent Bernie SandersBernard (Bernie) SandersSenators push HHS to negotiate lower prices on opioid overdose reversal drug New Zealand's female prime minister 'extremely angry' at Trump comparisons Dem senators unveil expanded public option for health insurance MORE. Joe Lieberman (I-Conn.) initially gave Democrats their 51st seat for the majority, but has since ended up embracing the GOP on many key issues. Still, Republicans are faring so poorly this year that they face an outside chance of falling below 41 seats. That would mean no filibusters — and that would end the GOP’s ability to stymie the Democratic agenda.

Democrats have a near-guaranteed pickup in Virginia and likely pickups in Alaska, Colorado, New Mexico and New Hampshire. Those five seats would bring the Democratic Conference to 55 seats. Democrats are running neck and neck against incumbent Republicans in Minnesota, North Carolina and Oregon. And they lag only slightly in Mississippi’s special-election seat.

If Democrats win those four attainable races, they’d reach 59 seats. That’s not a filibuster-proof majority, but large enough to reach 60 on an issue-by-issue basis. Senators like Maine’s Susan CollinsSusan Margaret CollinsTrump's NASA nominee advances after floor drama Family, friends mourn death of Barbara Bush Amid struggle for votes, GOP plows ahead with Cabinet picks MORE and Olympia Snowe, Arlen Specter of Pennsylvania, George Voinovich of Ohio and even Lieberman would likely defect frequently to the Democratic positions on issues of healthcare, labor, national security and energy.

But even if Democrats don’t reach 60 this year, their chances in 2010 are excellent. In fact, the 2010 map looks even better for Democrats than this year’s.

Sen. Sam Brownback of Kansas is retiring, and popular Democratic Gov. Kathleen SebeliusKathleen SebeliusTrump administration's reforms could make welfare work again Pro-dependency advocates miss the mark in attacking Kansas welfare reform Pence breaks tie to confirm Trump's pick for religious ambassador MORE will be available to make a run at the seat. Kentucky’s Jim Bunning barely escaped alive four years ago. Whether he retires or not, Rep. Ben Chandler (D) will be the favorite in 2010. New Hampshire Sen. Judd Gregg’s (R) conservatism is increasingly out of step with his state, which has been systematically cleansing itself of all things Republican. Watch for Rep. Paul Hodes (D) to challenge him.

In Ohio, Voinovich will have no shortage of Democrats looking for a sequel to the 2006 ouster of Republican incumbent Mike DeWine. And in Alabama, expect wildly popular Agricultural Commissioner Ron Sparks to challenge incumbent Sen. Richard Shelby (R). Sparks already regrets passing on this year’s Senate race, and won’t likely make the same mistake twice.

Moreover, rumors are swirling that Iowa’s Chuck GrassleyCharles (Chuck) Ernest GrassleySenate panel moving ahead with Mueller bill despite McConnell opposition Republicans refuse to back opioids bill sponsored by vulnerable Dem Pavlich: When will McCabe face prosecution for lying? MORE (R) might retire.

Freshman Republicans will face challenges in Alaska, Florida, Georgia, North Carolina, Oklahoma, South Carolina and South Dakota. Some of those challenges will be tougher than others, of course, but elected officials are most vulnerable during their first reelection battle, and Democrats will aggressively pursue these seats.

Even in Arizona, polling in 2007 suggested that popular Democratic Gov. Janet Napolitano could defeat longtime incumbent John McCainJohn Sidney McCainTrump's NASA nominee advances after floor drama Senate repeals auto-loan guidance in precedent-shattering vote Overnight Defense: Lawmakers worry over Syria strategy | Trump's base critical of strikes | Flake undecided on Pompeo | Coast Guard plans to keep allowing transgender members | GOP chair wants to cut B from Pentagon agencies MORE (R) in a battle of titans. And in Louisiana, Sen. David VitterDavid Bruce VitterPlanned Parenthood targets judicial nominee over abortion comments Trump nominates wife of ex-Louisiana senator to be federal judge Where is due process in all the sexual harassment allegations? MORE’s (R) sordid dalliances with prostitutes may provide an unexpected opening in a state that has been trending away from Democrats.

For their part, Democrats may have to sweat tricky reelection efforts in Colorado and Arkansas.

But barring any unexpected retirements or vacancies, 2010 — like 2008 — will be played almost exclusively on red territory.

The filibuster-proof majority is certainly within reach of Democrats — if not in this cycle, then in the next.

Moulitsas is founder and publisher of Daily Kos .