Two Crucial Rights for a Criminal Defendant
In determining which two rights a defendant receives at trial that are the most crucial, I thought about the accusations made against the defendant by the state and how crucial it is for a defendant to be able to provide a defense to the accusations. Because of this, it became obvious that the first crucial right to present for discussion should be the defendant’s right to confrontation. Specifically, the right to challenge witness testimony. 
The confrontation clause is an important right which is essential to ensuring a fair trial because issues raised by the prosecution’s direct examination of witness’s can be questioned by the defense during the cross-examination process. 
There are four stages of the witness examination. Relative to the prosecution’s witnesses, the defense benefits by being able to perform two of the four stages. Those two stages are: (1) the cross-examination, and (2) the re-cross examination. These two stages empower the defense to be able to: (1) challenge the credibility of the witness; (2) open the door for impeachment of the witness if the defense can show that the witness’s testimony is not factual, and (3) provides the defense an opportunity to provide some clarity as to the witness’s statements.  Especially, if such clarity is favorable to the defendant.
Courts have generally held that the ability of the defendant to cross examine pursuant to the confrontation clause must not be violated.  For instance, in Smith, even when the witness was a confidential informant in a narcotics case, Justice White cited that while the personal safety of the witness is a concern, the ability to cross examine the witness in situations where the line of questioning is normally permissible dictates that to violate the confrontation clause, the state must come forward to show why the cross examination should not be allowed. 
The second right in this discussion is the defendant’s right to double-jeopardy protection.
Double jeopardy is when a defendant who has either been convicted or acquitted is tried or punished for the same offense twice.  The Fifth Amendment of the U.S. Constitution guarantees that no citizen should face exposure to double jeopardy.  This is a most important right because without the prohibition against being tried twice for the same offense, the state could prosecute the individual as many times as required to obtain a conviction.
In essence, once a defendant is charged, the state could keep the individual under a perpetual threat of loss of life or liberty. An interesting aspect of double jeopardy is the Blockburger Rule. 
The Blockburger Rule defines what is meant by the term “same offense.” The rationale of the rule is that two separate offenses which require the satisfaction of the same elements to obtain a conviction would be classified as the “same offense” for the purposes of the double jeopardy clause. To clarify, crime (1), consisting of elements A-B-C is the same crime as crime (2), consisting of the same elements as crime (1), or any subset of elements. However, if crime (2) consisted of another element like element X, then the two offenses would be defined as different offenses. 
 John L. Worrall, Criminal procedure: from first contact to appeal 411 (2010).
 Id. at 412.
 Id. at 413.
 Smith v. Illinois, 390 U.S. 129, 88 S. Ct. 748, 19 L. Ed. 2d 956 (1968).
 Worrall, supra, at 419.
 U.S. CONST. amend. V.
 Worrall, supra, at 421.