The Patronus incident is the Ministry's (Fudge) excuse to get Harry expelled
by portraying Harry as a young out-of-control wizard.
Discrediting Harry would also discredit his claims that Voldemort has returned.
The patronus incident was perfect excuse to try and expell Harry
because the Ministry thought there were no witnesses to the appearance of the dementors
from book 5 order of the phoenix chapter number twelve, Grimmauld Place
“And of course, they didn’t report a word about the dementors
attacking you,” said Hermione. “Someone’s told them to keep that
quiet. That should’ve been a really big story, out-of-control dementors.
They haven’t even reported that you broke the International
Statute of Secrecy — we thought they would, it would tie in so well
with this image of you as some stupid show-off — we think they’re
biding their time until you’re expelled, then they’re really going to go
to town — I mean, if you’re expelled, obviously,” she went on hastily,
“you really shouldn’t be, not if they abide by their own laws, there’s no
case against you.”
also book 5 order of the phoenix chapter the hearing
“Dementors in Little Whinging?” Madam Bones said in tones of
great surprise. “I don’t understand —”
“Don’t you, Amelia?” said Fudge, still smirking. “Let me explain.
He’s been thinking it through and decided dementors would make a
very nice little cover story, very nice indeed. Muggles can’t see demen-
tors, can they, boy? Highly convenient, highly convenient . . . so it’s
just your word and no witnesses. . . .”
“I’m not lying!” said Harry loudly, over another outbreak of mut-
tering from the court.
The Ministry (Fudge) even went as far as changing the time of the hearing
in the hope that Harry would miss it and not be able to defend himself.
from book 5 order of the phoenix chapter the ministry of magic
“Oh Arthur!” he said desperately, without looking at Harry.
“Thank goodness, I didn’t know what to do for the best, whether to
wait here for you or not, I’ve just sent an owl to your home but you’ve
obviously missed it — an urgent message came ten minutes ago —”
“I know about the regurgitating toilet,” said Mr. Weasley.
“No, no, it’s not the toilet, it’s the Potter boy’s hearing — they’ve
changed the time and venue — it starts at eight o’clock now and it’s
down in old Courtroom Ten —”....
....“Why have they changed the time?” Harry said breathlessly as they
hurtled past the Auror cubicles; people poked out their heads and
stared as they streaked past. Harry felt as though he had left all his in-
sides back at Perkins’s desk.
“I’ve no idea, but thank goodness we got here so early, if you’d
missed it it would have been catastrophic!”
For the Tonks' spells i agree with Himarm and Anthony Grist
I suspect Ministry employees file some report when
they perform magic in the vicinity of young wizards. Otherwise you'd
get all sorts of false trace positives when Ministry employees do their jobs.
Arthur or Molly Weasley can admit to doing Tonks' spells in privet drive.
Under the guise of visiting their son's friend.
There is also a precedent for the Weasleys visiting Harry in his home.
The Ministry cannot use the Tonks incident. The Ministry
needs to pin a foolproof crime on Harry in order to discredit him
not a crime that can be explained by an "adult wizard family friend" visiting him in his home.
from book 4 goblet of fire chapter: Back to the burrow
“Ah, right,” said Mr. Weasley. “Better get cracking then.”
He pushed up the sleeves of his robes and took out his wand.
Harry saw the Dursleys draw back against the wall as one.
“Incendio!” said Mr. Weasley, pointing his wand at the hole in
the wall behind him.
Flames rose at once in the fireplace, crackling merrily as though
they had been burning for hours. Mr. Weasley took a small draw-
string bag from his pocket, untied it, took a pinch of the powder
inside, and threw it onto the flames, which turned emerald green
and roared higher than ever.
Harry did not receive a letter when Mr. Weasley performed this magic in front of
Harry and the Dursley's when he visited Harry to take him to the Quidditch cup
Also there would be no additional danger to Arthur or Molly because Fudge already suspects
the Weasley family.
from book 5 order of the phoenix chapter number twelve, Grimmauld place
“Trouble is, Fudge suspects Dad, he knows he’s friendly with Dum-
bledore, and he’s always thought Dad’s a bit of a weirdo because of his
Muggle obsession —”
“But what’s this got to do with Percy?” asked Harry, confused.
“I’m coming to that. Dad reckons Fudge only wants Percy in his
office because he wants to use him to spy on the family — and
Dumbledore.”
As for Moody, Tonks, Lupin, Shacklebolt etc. being discreet.
The reason for the discretion was that they did not want anyone to know
the location of the order of the phoenix headquarters,
Tonks' spells were performed in privet drive - far from the location of headquarters.
Any magic done in Harry's vicinity when they arrived at Grimmauld place would have triggered the trace and have the Ministry wondering what Harry was doing in Grimmauld place
from book 5 Order of the phoenix chapter: the advance guard
“We ought to double back for a bit, just to make sure we’re not be-
ing followed!” Moody shouted.
“ARE YOU MAD, MAD-EYE?” Tonks screamed from the front.
“We’re all frozen to our brooms! If we keep going off course we’re not
going to get there until next week! We’re nearly there now!”
Also, additional enchanted items that wont trigger the Trace
from book 7 Deathly Hollows
“We’re going to use the only means of transport left to us, the
only ones the Trace can’t detect, because we don’t need to cast spells
to use them: brooms, thestrals, and Hagrid’s motorbike.”
and from book 2 chamber of secrets chapter: the burrow
Dad came home and said you’d got an official warning for us-
ing magic in front of Muggles —”
“It wasn’t me — and how did he know?”
“He works for the Ministry,” said Ron. “You know we’re not sup-
posed to do spells outside school —”
“You should talk,” said Harry, staring at the floating car.
“Oh, this doesn’t count,” said Ron. “We’re only borrowing this.
It’s Dad’s, we didn’t enchant it. But doing magic in front of those
Muggles you live with —
Maybe as long as an item was enchanted with no children in the vicinity, then
that item can be used later on by underage wizards without activating the trace.
