Baker begins his memo by foreshadowing Trump accepting the party’s nomination at the Republican National Convention in July in Cleveland. He draws a historical comparison to Wendell Willkie, a businessman and political outsider who won the GOP nomination in 1940 but lost to Franklin D. Roosevelt, who secured his third term.

Baker writes that Republicans must “understand the changing environment and recalibrate now.” For instance, he writes, “Trump is saying that the Emperor has no clothes and he challenges our politically correct times. Our candidates shouldn’t miss this point.”

Baker explains how Trump has connected with voters, especially when it comes to trade with China and immigration. “Trump will continue to advance those messages, but you don’t have to go along with his more extreme positioning,” Baker writes. “Instead, you should stake out turf in the same issue zone and offer your own ideas.”

Addressing Trump’s controversial past statements about women, Baker writes, “Houston, we have a problem.”

“Candidates shouldn’t go near this ground other than to say that your wife or daughter is offended by what Trump said,” Baker adds. “We do not want to re-engage the ‘war on women’ fight.”

Although some of Baker’s recommendations are unique to the current environment, many are standard tactics employed in campaigns past, such as show¬casing “citizen narrators” or talking about “basic solutions” to policy problems to make candidates appear as accessible as Trump. This shows the conundrum the GOP is in: In grappling with Trump, it does not have many new tools at its disposal.

Time and again, Baker frames a future with Trump atop the ticket as an intense high-wire act for other Republicans. He calls Trump “a misguided missile” and says he “is subject to farcical fits.” With grim candor, Baker writes that he foresees a campaign year in which candidates repeatedly will have to fend off questions from reporters about the businessman’s comments and behavior.

“It is certain that all GOP candidates will be tied in some way to our nominee, but we need not be tied to him so closely that we have to engage in permanent cleanup or distancing maneuvers,” Baker writes, adding, “Don’t get drawn into every Trump statement and every Trump dust-up.”

Republicans, who hold a slim majority in the Senate, will be defending 24 seats next year, including in presidential battleground states where Democrats are mounting strong challenges. The most endangered GOP incumbents include Sens. Patrick J. Toomey (Pa.), Kelly Ayotte (N.H.), Rob Portman (Ohio), Ron Johnson (Wis.) and Mark Kirk (Ill.).

The task of protecting the majority has fallen to Baker, a retired Marine and Tennessee native. He was credited with many successes from the 2014 Senate campaigns and is close to such establishment fixtures as Senate Majority Leader Mitch McConnell (Ky.).

For months, veteran Republicans have been increasingly alarmed about the possibility of a Trump nomination. Sen. John McCain (R-Ariz.), who is up for reelection in 2016, acknowledged the anxiety Wednesday.

“Of course I worry. All of us have to worry about the viability of the top of the ticket,” McCain told reporters at a breakfast sponsored by the Christian Science Monitor.

McCain made an analogy to Barry Goldwater, a fellow Arizona senator who rallied the conservative grass roots to win the 1964 GOP nomination but lost in a landslide to Lyndon B. Johnson. “I think obviously we all know in history that when you have a weak top of the ticket, that has significant impact,” McCain said.

In his memo, Baker says Republicans should understand that Trump is riding a “reformist wave” sweeping the party’s ranks. It is partly ideological, he writes, but also driven by personality and aesthetics. He suggests that Senate incumbents and challengers should cast themselves as reformers.

Envisioning potential advertisements, Baker writes, “Feature candidates working on an old engine and note how sometimes you have to do a complete overhaul to get things working. Consider featuring a candidate in a field ripping up a rotten tree stump so the field can be cleared and planting can be done.”

Baker encourages campaigns to “up the vibe and change the look.”

“Voters are on to you when you do the standard walk and talk through a business, school, or factory,” he writes. He adds that candidates should “lose the suit and visit people in their homes and places of work.”

Baker also takes cues from Trump’s prolific use of social media to drive his message. “Promote tweets that push reforms or condemn Washington’s dysfunction,” he writes.

He warns against being distracted by Trump. “The Trump show may be going on, but back home our families are in a fight for their livelihoods,” he writes. “Always bring the campaign back home to real people and their daily struggle.”

Baker concludes the memo with a section titled, “Covering the Trump Bet,” which seems to throw cold water on the conventional wisdom that Trump will eventually fade.

“Trump has been gaining Democrat adherents and he’s solidifying GOP cohorts who feel they’ve been totally ignored by the Washington Ruling Class,” Baker writes. “If the environment aligns properly, Trump could win. It’s not a bet most would place now, but it could happen.”