Protestantism-based answer, intended to clarify the Christian disposition on the question, and on the idea of the Trinity.
First demographics. Christianity is a monotheistic faith, meaning simply, believers in it say so. Take a poll of Christians and exclude anyone who says they believe Jesus is now dead, or is/was not a real historical person. Ask those remaining whether the idea of the Trinity means that "there are three Gods", yes or no. I would be shocked if even a single person said yes out of a hundred.
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Secondly, the written teachings. I intepret the question before us as equivalent to asking whether Christian beliefs, the source of which is Yeshua (Jesus) himself, contradict the Shema Yisrael (Deuteronomy 6:4):
שְׁמַע, יִשְׂרָאֵל: יְהוָה אֱלֹהֵינוּ, יְהוָה אֶחָד.
Yeshua himself answered this quite directly in Yochannan (John) 10:30. Most English editions have:
I and my Father are one.
The "one" here being usually translated from Greek, or sometimes Latin, but corresponding to echad (אֶחָד) from above. The Aramaic versions used in the Eastern Orthodox tradition have (open license font):
ܐܸܢܵܐ ܘܐܵܒ݂ܝ. ܚܲܕ݂ ܚܢܲܢ
We have ܚܲܕ݂ khad for "one". We know this to be a cognate of Hebrew אֶחָד echad because the Shema Yisrael is directly quoted in Mark 12:29:
ܐܵܡܲܪ ܠܹܗ ܝܼܫܘܿܥ. ܩܲܕ݂ܡܵܝ ܡܸܢ ܟܠܗܘܿܢ ܦܘܼܩܕܵܢܹ̈ܐ ܫܡܲܥ ܝܼܣܪܵܝܼܠ܅ ܡܵܪܝܵܐ ܐܲܠܵܗܲܢ ܡܵܪܝܵܐ ܚܲܕ݂ ܗ̄ܘܼ.
Yeshua said to him, The first of all the commandments is, Shema Yisrael, MARYA [corresponds to YHWH] Aloha is one MARYA...
The khad is the same in both places. So clearly, he teaches that God is one (echad), and he is one (khad) with the Father. And he directly debates this very question in the conversations in the Temple that John / Yochannan and Mark recorded in their gospels.
Of course, a great many people do not believe that Yeshua is one with the Father, but I argue that for those who do, based on the literal text of the teaching itself, that belief cannot possibly be in contradiction to the Shema Yisrael.
Now to consider today's doctrines.
Within Christianity a common analogy for the Trinity is the shamrock: one plant with three distinct leaves. (Another answer here mentions the hydra. That's the same idea I suppose, but you won't hear many Christians use that analogy for the Trinity, for reasons.)
Not all official statements of faith discuss the Trinity explicitly, but here are some that do:
There are also a number of groups, some of them large, that reject the Trinity.
Specifically with Catholicism, other questions could be in play, because many Catholics pray to their "Saints" as proxies, asking the Saints to pray to God on their behalf. Many Protestants consider this practice to be idolatry. This is, in fact, one aspect of one of the critical doctrinal divides between Catholics and Protestants. I do not know how most Orthodox traditions treat this particular issue.