Ms Palin is the only Republican in recent history to demonstrate the kind of star power that has elevated Mr Trump to the top in the race for the 2016 Republican presidential nomination. Mr Trump regularly draws crowds numbering in the thousands - just as Ms Palin did after Senator John McCain chose her to be his vice-presidential running mate in 2008.
Both Mr Trump and Ms Palin also have complementary political outlooks and appeal to the same segment of the Republican primary electorate - non-college educated, largely working class whites who are disillusioned with professional politicians and Washington politics in general. These voters view the scorn of the establishment elite - which has been heaped, at times, on both Ms Palin and Mr Trump - as a badge of honour rather than a weakness.
For some Republican candidates, an endorsement from Ms Palin could alienate their support among party leaders who question Ms Palin's intellect and interest in governing. In Mr Trump's case, however, these Republican elders and Washington pundits have long since turned against his campaign.
Even the speaking styles of Mr Trump and Ms Palin - unvarnished and informal, relying on rhetoric and not policy details - are similar.
Last January Ms Palin - who was then reportedly mulling her own bid for the 2016 Republican nomination - delivered a much-derided speech during a Republican forum in Iowa that drew many other presidential aspirants.
It's worth another listen. Her presentation was dismissed as unfocused and at times incoherent, more akin to a stream of consciousness rather than the traditional set-pieces delivered by others on the stage.
In hindsight, however, it was exactly the kind of monologue that Donald Trump has given day after day since he launched his campaign - and his supporters love him for it.
The two even have drawn from the same pool of political staff. Michael Glassner, the Trump campaign's national political director, served as chief of staff for Ms Palin's political action committee.
But how valuable is Ms Palin's support for Trump? While the former Alaska governor's reputation has been diminished since the heady days of 2008 - thanks to her absence from public office and involvement in series of questionable reality television shows - she is still well-liked by conservative Republicans and nearly universally known.
Her backing could help insulate Mr Trump against charges that he's not a true believer in the cause due to his support for liberal political issues and candidates in the past. At the very least, she could had have even more crowd-drawing power to a Trump campaign that already fill entire sports arenas.
To best understand the potentially ground-shifting implications of the Trump-Palin entente, however, observe how the campaign of Ted Cruz, the candidate closest to Mr Trump in the polls, has reacted.
"Sarah Palin has been a champion for the conservative cause, and if she was going to endorse Donald Trump, sadly, she would be endorsing someone who's held progressive views all their life on the sanctity of life, on marriage, on partial-birth abortion," Cruz campaign spokesman Rick Tyler told a television interviewer on Tuesday when rumours of a Palin endorsement first surfaced. "Donald Trump claims he's changed all those views. But I think if it was Sarah Palin - let me just say, I'd be deeply disappointed."
Leon Wolf, a blogger on the conservative RedState blog was even more dismayed.
"There is literally no excuse for Sarah Palin not to endorse Ted Cruz, if she believes even half the things she's been saying over the years about mavericks and people who have taken on entrenched Republican interests," he writes. "Donald Trump has done none of this."
He ascribes the endorsement to Ms Palin's desire to profit from Mr Trump's recent popularity.
Dismissing Ms Palin's support as irrelevant or misguided could prove a tricky line of attack for Mr Cruz and his supporters, however.
Texas Senator Ted Cruz surged to national prominence due in large part to the grassroots conservative Tea Party movement that Ms Palin helped inspire. In his book, he credits her endorsement as contributing to his upset Senate win in 2012 over a better-known, better-financed establishment Republican candidate.
"In a Republican primary, everyone claims to be conservative and voters are pretty cynical," Mr Cruz told Mike Allen of Politico in August 2012. "I think conservatives trust Sarah Palin that if she says this guy is a conservative, that he is a real deal."
Ted Cruz believed that about Ms Palin in 2012. Will Republican voters who might otherwise support Mr Cruz - in Iowa and elsewhere - follow her into Trump's ranks today?
Republican candidates in, and out, of the 2016 presidential race
Sarah Palin's endorsement of Republican presidential frontrunner Donald Trump on Tuesday night was billed as a surprise, but in hindsight it is surprising only that it took so long for this natural political partnership to be forged.