It seems reasonable that if Texas pushed it, Cruz is guilty of fraud, having run as and taken the position of Senator for the State of Texas as a dual citizen.
The Constitution requires a Senator to be a citizen of the United States for 8 years I believe.
He was a citizen of the US since the day he was born.
You really need to learn to use a search engine. I found the correct info in less than 15 seconds. Here it is and shame on you for passing on false info...
THE TEXAS CONSTITUTION
ARTICLE 3. LEGISLATIVE DEPARTMENT
Sec. 6. QUALIFICATIONS OF SENATORS. No person shall be a Senator, unless he be a citizen of the United States, and, at the time of his election a qualified voter of this State, and shall have been a resident of this State five years next preceding his election, and the last year thereof a resident of the district for which he shall be chosen, and shall have attained the age of twenty-six years.
http://www.statutes.legis.state.tx.us/Docs/CN/htm/CN.3.htm