Republicans are concerned that former senator Russ Feingold (D), above, can take the seat of Ron Johnson (R), a first-term senator, in Wisconsin. (Joe Koshollek/AP)

Longtime Republican strategists and campaign consultants privately acknowledge they are so certain of Hillary Clinton’s victory — and so worried about its impact on Senate races and GOP control of the chamber — that they are already considering a controversial tactic that explicitly acknowledges Donald Trump’s defeat.

The tactic, used by congressional Republicans two decades ago, late in the 1996 campaign, involves running television ads that urge voters to elect a Republican Congress so Clinton won’t have “a blank check” as president.

“The advice to candidates to stress the ‘blank check’ argument is being offered [by field workers from the National Republican Congressional Committee] to Republican candidates who are running below 50 percent in their own polling,” wrote Adam Clymer of the New York Times in late October 1996.

[To save the Senate, Mitch McConnell’s Republicans may have to run against Clinton]

Clymer noted that an unnamed GOP aide assured campaigns “that the national Republican headquarters will not be angry with them or cut off their campaign funds if they concede that Mr. Dole will lose and they tried to save themselves.”

Republicans held their House majority that year, losing only three seats even though Bill Clinton beat Bob Dole by 8.5 points.

Some operatives believe “blank check” ads could begin this year as early as right after Labor Day, while others expect Republican campaigns to hold off until as late as mid-October.

“We all believe that Trump will be a drag on the rest of the ticket. The only question is whether he’ll be bad or horrific,” said one highly regarded GOP strategist with a long list of election victories under his belt who did not want to speak ill on the record of the GOP presidential nominee.

With a little more than four months to go until Election Day, the fight for the Senate is likely to turn on whether a handful of incumbent Republicans can localize their races to run well ahead of their party’s presidential nominee.

Two Republican Senate seats are already in critical condition.

Mark Kirk of Illinois won six years ago in near ideal circumstances, and while he is running as far away from Trump as he can, Illinois simply is too Democratic for him to survive.

Also in desperate shape is Wisconsin’s Ron Johnson, who often acts as if he knows all the answers and doesn’t want to hear other opinions. Johnson defeated then-Sen. Russ Feingold six years ago, but polling shows Johnson trailing in the rematch and most Republicans are pessimistic about the outcome.

If those two seats flip, New York Democrat Chuck Schumer must net just two more seats to become the next majority leader, assuming that Hillary Clinton wins the White House.

None of the next three Democratic opportunities is a sure thing.

New Hampshire’s Kelly Ayotte fits the Granite State well and is seen as a top priority by Republicans, who regard her as thoughtful, likable and an important asset in a party made up disproportionately of older white men.

But the state’s competitiveness and the quality of the Democratic challenger, Gov. Maggie Hassan, combine to put Ayotte at great risk. While GOP strategists believe that Ayotte has greater appeal than Hassan, they acknowledge that a very poor showing by Trump in the state could all but doom Ayotte.

Republicans have the better candidate in Ohio, where Democratic former governor Ted Strickland, who turns 75 in August, is challenging GOP incumbent Rob Portman, 60.

Strickland, who once represented southeast Ohio in Congress, fared well politically in part by running as a socially conservative Democrat. But his party’s stance on coal and Strickland’s record give Republicans and their business allies plenty of ammunition.

[Read more Political Stu]

Portman’s support for same-sex marriage gives him a path to attract swing voters, but his résumé — member of Congress, U.S. trade representative and director of the Office of Management and Budget — presents Democrats with obvious lines of attack.

Strickland seemed to have a clear if not overwhelming lead over Portman in the spring and summer of 2015, but more-recent polls suggest the Republican is no worse than even and probably has a slight advantage. Still, Ohio is competitive, and if Trump proves weak, Portman may not be able to overcome that deficit.

In Pennsylvania, Pat Toomey won election six years ago in a squeaker. Republican operatives rave about his campaign and argue that challenger Katie McGinty’s weakness on the stump and thin electoral history (she finished fourth in the Democratic primary for governor two years ago) demonstrate that she is a weak challenger. Moreover, Pennsylvania is one state where Trump could overperform, possibly helping Toomey.

But the Keystone State is likely to be very competitive, and Republicans have not carried the state since 1988, even though they argue every election cycle that Pennsylvania is in play.

Finally, Florida looked like a Democratic advantage until Sen. Marco Rubio announced he would run for reelection and a Miami television station aired a two-part segment that strongly suggested that the likely Democratic Senate nominee, Rep. Patrick Murphy, is an empty suit who embellished his résumé. (The National Republican Senatorial Committee has spent heavily on opposition research the past two cycles.)

Rubio has a competitive primary against a wealthy businessman running against Washington, and the freshman senator picked up a good deal of political baggage over the past year. But his candidacy does improve Republican chances of holding the seat.

While four states with at-risk GOP incumbents — New Hampshire, Ohio, Pennsylvania and Florida — could well determine Senate control, Nevada is the lone Democratic headache.

Opinion is deeply divided about the Silver State. Rep. Joe Heck (R) has proved his mettle by winning a competitive district repeatedly, even when President Obama carried it. But Democrat Catherine Cortez Masto, the state’s former attorney general, is a personable Hispanic hopeful who has the complete support of the retiring Harry Reid.

Both parties are surprisingly optimistic about the race, but some Republicans have reservations about Heck’s team and note that Republican Dean Heller barely nosed out Shelley Berkley in the state’s 2012 Senate election. The environment is worse now, and Masto has more appeal than Berkley did, they add.

While Democrats believe that a number of second-tier Senate opportunities could develop, two stand out: Arizona and North Carolina.

Sen. John McCain of Arizona has a primary to win before facing Rep. Ann Kirkpatrick (D). He continues to be a strong campaigner, and Kirkpatrick does not ooze charisma. But the state’s large Latino population is something of a wild card, and the race starts off surprisingly close.

In the Tar Heel State, Sen. Richard Burr must be concerned that Democratic challenger Deborah Ross can ride a Clinton wave in a state Obama carried in 2008.

GOP strategists feel good about their ability to localize races and demonize Democratic challengers with opposition research. And some Republicans argue that Trump is his own brand, which will allow their party’s Senate candidates to run apart from the top of the ticket. That may be true — or it could be nothing more than wishful thinking.

For now, Democrats are only a slight favorite to win at least four seats in November. But Trump is a very dangerous wild card for his party, and larger Democratic gains certainly are possible.